Version May 2024
INTRODUCTION — Squamous cell carcinogenesis in the mucosa of the head and neck involves the progressive accumulation of a large series of genetic abnormalities in genes regulating cell cycle progression, mitogenic and differentiative signaling pathways, angiogenesis, and cell death. This mutagenic progression, called multistep carcinogenesis, parallels the genetic model of colorectal carcinogenesis [1,2]. (See "Molecular genetics of colorectal cancer".)
Evidence for a mutational progression in tumorigenesis of head and neck squamous cell carcinoma (HNSCC) first derived from cytogenetic studies that demonstrated nonrandom clonal losses, duplications, and rearrangements of chromosome segments in head and neck tumors [3-5]. Within many of these regions of recurring chromosomal abnormality, candidate oncogenes or tumor suppressors have since been identified, some of which appear to play critical roles in carcinogenic transformation. Subsequent detailed progression models for carcinogenesis of the head and neck have been based on mutational models and differential gene expression [6,7]. Using contemporary sequencing technologies, we have developed a better understanding of the mutational landscape in HNSCC [8-10].
Identifying critical genetic events that lead to the development of head and neck cancer has further clarified the molecular basis for specific risk factors, such as tobacco and alcohol, as well as human papillomavirus (HPV) infection. This information has become critical for risk stratification and may result in modifications to standard treatment paradigms. (See "Epidemiology and risk factors for head and neck cancer" and "Epidemiology, staging, and clinical presentation of human papillomavirus associated head and neck cancer".)
In addition, these studies have unveiled a new series of targets for chemotherapeutic and chemopreventive intervention, which ultimately may result in more rational and successful therapies for this disease. (See "Chemoprevention and screening in oral dysplasia and squamous cell head and neck cancer".)
FIELD CANCERIZATION — The term field cancerization was first used to describe observations from microscopic examination of 738 lip, oral cavity, and pharyngeal carcinomas [11]. The grossly normal epithelium adjacent to the cancer in this study frequently contained dysplasia, carcinoma in situ, or invasive carcinoma, as though the entire mucosal field had been damaged and preconditioned by a carcinogen.
The molecular basis for field cancerization has been studied by evaluating matched dysplastic and malignant lesions within the oral cavity for genetic alterations [12]. Two important observations were made:
●Four of the 15 dysplastic lesions harbored the same genetic abnormalities detected in the tumor. The finding of identical genetic lesions in dysplastic lesions and invasive cancer in the same patient provided further evidence that dysplasias were precursor lesions and that multiple lesions can arise due to the lateral migration of genetically altered cells through the oral mucosa (a phenomenon termed clonal cancerization [13]).
●Eight of the 15 dysplastic lesions showed genetic alterations not found in the matched cancer. This provided evidence that multifocal disease can arise from the development of several genetically altered clones from different initiating events.
The importance of dysplastic lesions as precursors to malignancy was illustrated in a retrospective study of 97 cases of epithelial dysplasia in the head and neck region [14]. Fifty patients developed a squamous cell carcinoma in the same area as the dysplastic lesion at a mean follow-up of 30 months.
Support for field cancerization is also provided by the development of second or multiple primaries in patients with head and neck squamous cell carcinoma. Cancer at one site in the head and neck is a strong predictor for the development of a second primary tumor elsewhere. Second tumors can either occur at or close to the same time as the primary lesion (synchronous), or at least six months later (metachronous). As with dysplasia, the second tumors may be clonally similar to or distinct from the primary tumor. (See "Overview of the diagnosis and staging of head and neck cancer", section on 'Incidence of second and multiple primaries'.)
GENOMIC ALTERATIONS AND MULTISTEP CARCINOGENESIS — Multistep carcinogenesis describes the series of events (initiation, promotion, progression) that leads to the development of invasive carcinoma. Although the specific sequence of genetic events has not been defined, numerous molecular mutations and genetic alterations have been found in both carcinomas and premalignant tissue.
A large number of studies examining chromosomal abnormalities in head and neck squamous cell carcinoma (HNSCC) serve as the foundation for current models of squamous cell carcinogenesis and indicate the complexity of the transformation process. Cytogenetic analysis and more detailed loss of heterozygosity studies based on microsatellite analysis have demonstrated that particular chromosomal abnormalities are consistently observed in HNSCC. Among many others, regions found to be commonly lost include 9p21 (the site of the p16 CDKN2A and p14 ARF tumor suppressor genes), 9p34 (NOTCH1 tumor suppressor or oncogene) [8], 17p13 (site of the p53 tumor suppressor gene and perhaps another tumor suppressor that remains to be identified), 11p15 (HRAS oncogene) [15], 3q26 (PIK3CA oncogene) [8], 10q23 (PTEN tumor suppressor gene) [16], 3p (the site of potential tumor suppressor genes, including FHIT and RASSF1A), 13q21 (unknown tumor suppressor near the retinoblastoma locus) [6,17,18], 18q21 (the site of the DCC gene) [19], and 5p (site of the TERT gene promoter) [20].
One study performed microsatellite analysis on a series of hyperplastic lesions, dysplastic lesions, carcinomas in situ, and invasive squamous cell carcinomas, examining these and other chromosomal loci [6]. The findings generated the first model of sequential genetic progression in head and neck squamous cell carcinogenesis, as illustrated in the figure (figure 1) [21]:
●Loss of 9p, leading to inactivation of the p16 tumor suppressor gene, was a very early event, occurring even in transition from normal to hyperplastic mucosa. Deletion involving the 9p21 locus is found in 70 percent of all HNSCC [22].
●This was frequently followed by loss of 3p and 17p in transition to dysplasia [21]. Among other putative tumor suppressors, 17p includes the p53 gene. The transition from dysplasia to carcinoma in situ was frequently associated with specific additional losses (11q, 13q, 14q) and still others (6p, 8, 4q) in the transition to invasive squamous cell carcinoma.
●Despite early loss of 17p in this model, sequencing of p53 alleles indicated that loss of p53 function may occur significantly later in the course of malignant transformation.
These data were confirmed and extended by using comparative genomic hybridization, a technique that permits concurrent analysis of genetic gain and loss throughout the genome. When well-differentiated and poorly differentiated HNSCC were evaluated by this technique, there was evidence of genetic progression from well to poorly differentiated cancer [23]:
●Well-differentiated tumors consistently demonstrated underrepresentation (loss) of chromosomes 3p, 5q, and 9p, together with overrepresentation (gain) of 3q.
●Poorly differentiated tumors typically shared these aberrations but had other abnormalities, such as evidence of deletion of 4q, 6q, 8p, 11q, 13q, 18q, and 21q and overrepresentation of 1p34-pter, 11q13, 19, and 22q.
The inactivation of tumor suppressor genes by epigenetic mechanisms has now been reported in HNSCC. Promoter hypermethylation as a mechanism of tumor suppressor gene inactivation has been noted with the DCC gene, the retinoic acid receptor (RAR)-beta2, P16, and the O6-methylguanine-DNA methyltransferase (MGMT) gene [19,24].
These arrays of genomic alterations underscore the complexity of carcinogenic transformation and are consistent with studies in other tumor models, suggesting that many genetic alterations, perhaps involving 10 or more genes, are necessary for fully malignant growth [25]. There is great interest in defining the extent to which individual molecular markers dictate prognosis in HNSCC [26,27].
The Cancer Genome Atlas (TCGA) profiled 279 HNSCC specimens and evaluated the DNA/RNA structural alterations, somatic mutations, genomic alterations by site, stage, human papillomavirus (HPV) status, molecular subtypes, and putative biomarkers. This study is the most comprehensive integrative genomic analysis of HNSCC. With HPV associated tumors, the loss of TRAF3, activating mutations in PIK3CA, and amplification of E2F1 were more common. With non-HPV associated tumors, co-amplification of 11q13 and 11q22, focal deletions in nuclear the set domain gene/tumor suppressor genes, and focal amplifications in receptor tyrosine kinases were more common. The figure highlights the frequency of genetic alterations for HPV associated and non-HPV associated tumors (figure 2) [28].
Next-generation sequencing of 252 formalin-fixed, paraffin-embedded HNSCC tumors found the most common alterations to be PIK3CA in HPV associated tumors and TP53 and CDKNN2A/B in the non-HPV associated tumors. In HPV associated tumors, several alterations along the PI3K pathway were present, including alterations of PTEN, AKT1, RICTOR, mTOR, AKT2, and PIK3R1, in addition to PIK3CA [16].
Next-generation sequencing in 53 patients with advanced HNSCC showed that recurrent and/or metastatic non-HPV associated and HPV associated tumors had similar mutation counts and copy number-altered fraction of genome [29], unlike other studies that suggested higher mutational burden in non-HPV associated primary tumors. As compared with HPV associated tumors, non-HPV associated tumors had more frequent alterations in TP53, TERT promoter, and CDKN2A. Additionally, the mutational profile of advanced non-HPV associated tumors closely resembled non-HPV associated primary tumors sequenced by TCGA, whereas the mutational profile of HPV associated tumors demonstrated profiles that were intermediate between HPV associated and non-HPV associated tumors sequenced by TCGA. Advanced (ie, recurrent and metastatic) HPV associated tumors were consistently found to have higher frequencies of TP53 mutations and lower frequencies of PIK3CA mutations compared with primary HPV associated tumors [20,29,30]. These findings provide insight into HNSCC genomic alterations based on HPV status and disease setting.
DISRUPTION OF MITOGENIC SIGNALING PATHWAYS — Mitogenic signaling pathways initiated through cell surface receptors are disrupted in most cancers, including head and neck squamous cell carcinoma (HNSCC). Dysregulated factors have included both downstream signaling molecules, such as Ras [31], and a number of transmembrane receptors and their ligands. Particular attention has been focused on the epidermal growth factor receptor (EGFR) as a factor in carcinogenesis and as a therapeutic target, as well as the closely related human epidermal growth factor receptor 2 (HER2 [c-erbB-2]) receptor [32-39]. Both of these receptors have cytoplasmic domains with tyrosine kinase activity and activate a number of intracellular second messenger pathways.
EGFR and transforming growth factor-alpha — Both EGFR and its principal ligand, transforming growth factor (TGF)-alpha, are upregulated in HNSCC, constituting an autocrine activation loop [36]. TGF-alpha overexpression is frequently induced relatively early in carcinogenesis, being elevated in mild dysplasia, with no further increases in advanced dysplasias or carcinoma. In contrast, EGFR expression usually increases progressively with increasing degree of dysplasia and is markedly elevated in many fully transformed HNSCCs [32,36]. EGFR appears to be upregulated to some extent in more than 90 percent of HNSCCs [33,34]. High EGFR levels in HNSCC, as assessed by either protein expression or gene copy number, are associated with shorter overall and progression-free survival [40]. In addition, clinical studies have confirmed the importance of EGFR as a therapeutic target for HNSCC [41] with cetuximab as the only US Food and Drug Administration (FDA)-approved targeted therapy in HNSCC. (See "Treatment of metastatic and recurrent head and neck cancer".)
Ras-mediated pathway: Raf/MEK/ERK and PI3K — The Ras family includes three genes: HRAS, KRAS, and NRAS. In HNSCC, these tumors exhibit exclusively HRAS mutation, which is seen in 35 percent of oral cancers in India [42,43]. In the United States, this is not as common and is seen in only 4 to 5 percent of HNSCC tumors [9,10]. RAS mutations activate the Raf/MEK/ERK pathway and the PI3K pathway, both of which are involved with cell proliferation, differentiation, and cell survival. In HNSCC, overactivation of the PI3K pathway occurs by PI3KCA mutation, which is seen in 6 to 8 percent of cases, or PTEN loss, which is seen in 10 percent of tumors [44,45]. RAS mutations and PIK3CA amplifications, not PIK3CA mutations, have been associated with poorer progression-free survival [30].
Several clinical trials targeting the PI3K pathway, as a single agent or in combination, are ongoing. Other trials are evaluating the use of a farnesyltransferase inhibitor in HRAS mutant head and neck cancer. (See "Treatment of metastatic and recurrent head and neck cancer", section on 'Investigational approaches'.)
HER2 gene product — The HER2 gene product (also known as c-erbB-2) has extensive structural homology to EGFR and is overexpressed in many solid tumors, including breast, lung, ovarian, and gastric cancers. In all of these sites, HER2 overexpression has been identified as a negative prognostic factor. Upregulation of HER2 occurs in approximately 50 percent of all HNSCCs [37,38]. In addition to its role in mitogenesis, HER2 signaling is thought to increase metastatic potential through induction of a diverse collection of factors involved in altering cell-cell adhesion and invasiveness. Like EGFR, HER2 expression has been correlated with decreased overall survival in HNSCC in many [39,46,47], but not all, studies [48].
Src kinase — Since the discovery of EGFR and targeted agents that inhibit the EGFR, research has been focused on mechanisms of resistance to EGFR inhibitors. One emerging target is the nonreceptor kinase src, a downstream component of the EGFR signaling complex [49]. Activated src phosphorylates the intracellular domain of EGFR and mediates the activation of the STAT3 pathway by EGFR [50]. Src kinase is also integral to GRP-induced EGFR activation and downstream signaling via the mitogen-activated protein kinase (MAPK) pathway. In one study, targeted inhibition of src family tyrosine kinase activity resulted in decreased GRP-induced EGFR activation and MAPK phosphorylation [51].
Constitutive activation of src may mediate resistance to EGFR inhibitors, and resistance might be overcome clinically by combined inhibition of both targets, src and EGFR. Among small-molecule tyrosine kinase inhibitors in clinical development, dasatinib and saracatinib inhibit the src family kinase activity in a highly selective manner [52,53]. Phase I/II trials targeting the src pathway and EGFR pathways in patients with HNSCC are ongoing.
DISRUPTION OF CELL CYCLE CONTROL — Many of the factors that are known to play a critical role in regulating cell cycle entry (particularly cyclin D1, the p16 cyclin-dependent kinase [CDK] inhibitor, p53, and c-myc) are dysregulated in head and neck squamous cell carcinoma (HNSCC).
Overexpression of cyclin D1 — Overexpression of cyclin D1, encoded by CCND1, has been observed in HNSCC. Cyclin D1 pairs with CDK4 and CDK6 to promote cell cycle progression in the G1-S transition, which is critical to commitment to replication and division [54]. CCND1 polymorphism, thought to alter cyclin D1 expression, has been associated with HNSCC risk, tumor grade, tumor recurrence, and survival [55-59].
Inactivation of the p16/p14 ARF locus — p16 (CDKN2/MTS1) and p14 ARF are overlapping genes in the same locus, encoded by distinct open reading frames and distinct mRNA splice forms. Inactivation of this locus is the most common genetic alteration that has been described in HNSCC [60]. The gene product p16 is a potent inhibitor of both CDK4 and CDK6. Thus, inactivation of p16, as with overexpression of cyclin D1, increases CDK4/6 activity and promotes cell proliferation. On the other hand, re-expression of p16 in HNSCC cells results in significant antitumor effects, both in tissue culture and in animal models [61,62]. p14 ARF blocks association of p53 with its inhibitor MDM2. Thus, loss of p14 ARF leads to indirect inhibition of p53 function.
Inactivation of p53 tumor suppressor gene — p53 is a critical antineoplastic factor, suppressing aberrant proliferation, both by inhibition of cell cycle progression and by induction of apoptotic cell death. The regulation of cell cycle by p53 is mediated primarily at the G1-S transition, both through transcriptional induction of cell cycle inhibitors, such as p21, and through transcription-independent mechanisms that are poorly understood.
The p53 gene is inactivated in at least one-half of HNSCCs [63-70], although some reports suggest that the mutation rate is higher, approaching 80 percent [71]. The timing of p53 inactivation in HNSCC tumorigenesis is controversial, with some reports demonstrating aberrant expression in early dysplasia and the majority suggesting mutation only late in tumor evolution [6,63-65]. The mechanism underlying loss of p53 expression depends on the risk factor for the development of HNSCC [72,73]. Loss of p53 expression through mutations or loss of heterozygosity is associated with a history of alcohol and tobacco use. As an example, in one study of 129 patients with primary HNSCC, p53 mutations were found in tumor samples in 58 percent of those who both smoked and used alcohol, in 33 percent who smoked but abstained from alcohol, and in 17 percent who neither smoked nor drank alcohol [72].
In contrast, there is an inverse relationship between the presence of p53 mutations and human papillomavirus (HPV) infection. In the setting of HPV infection, p53 is inactivated by binding to the E6 viral protein. (See 'Human papillomavirus' below.)
Prognostic impact — Mutations in the p53 gene may also influence prognosis and response to treatment in both localized and locoregionally advanced HNSCC [70,74-78]:
●In a study of 105 patients with locoregionally advanced head and neck cancer, the presence of a p53 mutation was associated with a statistically significant 70 percent less chance of responding to neoadjuvant chemotherapy as compared with wild-type p53 [77]. (See "Locally advanced squamous cell carcinoma of the head and neck: Approaches combining chemotherapy and radiation therapy".)
●The correlation between p53 mutations and outcome after surgical treatment was addressed in a retrospective analysis of 420 patients who underwent curative intent surgery for head and neck cancer on a prospective multicenter trial [70]. The mutations were classified as disruptive or nondisruptive based on the degree of predicted disturbance of the p53 protein structure. Patients whose tumors harbored p53 mutations (53 percent of all patients) had significantly reduced overall survival after surgical treatment compared with those with wild-type p53 (hazard ratio [HR] for death 1.4) [70]. The association was strongest for disruptive mutations (HR for death 1.7).
●The association between p53 mutations and response to larynx-preserving surgery was studied in a series of 71 patients with locoregionally advanced head and neck cancer who were treated on larynx-preserving protocols [78]. Tumors were assayed for immunohistochemical expression of p53, its upstream regulator MDM2, and its downstream transcriptional target p21/WAF1. In a multivariate analysis, no molecular marker significantly predicted the response to induction chemotherapy. However, compared with those with wild-type p53, patients with p53 positive tumors had significantly worse five-year survival (29 versus 51 percent) with larynx preservation.
●Although p53 mutations are infrequent in HPV associated disease, complete inactivation of p53 in HPV associated HNSCC cell lines was associated with resistance to radiation therapy and aggressive tumor behavior [79].
NOTCH-1 gene — Mutations with the NOTCH-1 gene were noted in 15 and 14 percent of HNSCC in two studies with next-generation sequencing [9,10]. NOTCH-1 is believed to play a role in regulating normal cell differentiation and has both oncogenic and tumor suppressor activity [9,42]. In HNSCC, NOTCH-1 appears to act as a tumor suppressor gene, and the majority of the mutations are likely loss of function mutations that affect the epidermal growth factor (EGF)-like ligand binding domain or the NOTCH intracellular domain (NICD). Therapeutically targeting NOTCH-1 in HNSCC is an evolving field.
c-myc oncogene — The c-myc oncogene is a potent proliferative factor that, when overexpressed, can promote G1-S transition by mechanisms that have not been defined. Amplification of the c-myc locus occurs frequently in HNSCC, and c-myc upregulation has been correlated with decreased overall survival [80,81].
TERT gene promoter — The telomerase reverse transcriptase (TERT) gene encodes the reverse transcriptase subunit of telomerase that maintains the telomere length through synthesis of telomere units at the ends of chromosomes. In one study, approximately 75 percent of oral cavity squamous cell carcinomas exhibited TERT promoter mutations C228T and C250T [20]. Another report detected TERT mutations in 34 percent of HNSCC tumors, predominantly among oral cavity cancers [82]. TERT mutations were also more prevalent in advanced non-HPV associated tumors than non-HPV associated primary tumors [29]. The prognosis of a TERT mutation has been associated with a significant decrease in disease-free survival and overall survival [82].
Human papillomavirus — Oncogenic viruses are another factor that can affect cell cycle regulation. In situ hybridization and polymerase chain reaction (PCR)-based detection have demonstrated that as many as one-third of all HNSCCs and 60 percent of oropharyngeal cancers contain HPV, with the majority of these containing high-risk oncogenic HPV types 16, and fewer contain HPV types 18 or 33. The molecular profile of HPV associated HNSCCs is distinct from those that are non-HPV associated, with almost all HPV associated tumors expressing wild-type tumor suppressor genes p53 and p16. This would suggest different mechanisms of oncogenesis for HPV associated as compared with non-HPV associated tumors, and that HPV infection is an early event in head and neck squamous cell carcinogenesis. (See "Epidemiology, staging, and clinical presentation of human papillomavirus associated head and neck cancer", section on 'Biology of HPV'.)
HPV associated head and neck cancers respond more favorably to regimens using chemotherapy and radiation therapy than do those with non-HPV associated tumors. These data are discussed in detail elsewhere. (See "Epidemiology and risk factors for head and neck cancer", section on 'Human papillomavirus' and "Treatment of human papillomavirus associated oropharyngeal cancer".)
DISRUPTION OF CELL-CELL CONTACT AND DIFFERENTIATION PATHWAYS — Cellular differentiation is, in part, regulated by a transcriptional program determined by expression of nuclear retinoic acid receptors. Retinoic acid receptors are bipartite transcription factors composed of RAR and RXR components, and multiple members of both the RAR and RXR families can associate to differentially regulate arrays of downstream targets.
Histologic progression in premalignant dysplastic lesions of the head and neck has been associated with loss of nuclear RAR-beta expression [83]. Treatment of such lesions with 13-cis retinoic acid can result in recovery of normal nuclear RAR-beta expression and may lead to re-establishment of a normal differentiation program in the affected mucosa [84,85]. These observations have spawned an enormous interest in retinoid research, particularly among investigators interested in chemoprevention.
E-cadherin — Epithelial tissue structure is dependent on a complex network of cell-cell adhesions, and loss of cell-cell contact has been associated with tumor invasiveness and metastatic potential in many cancers. One of the critical factors in these networks that has been most clearly linked to cancer progression is E-cadherin (CDH1). Invasion in an E-cadherin negative tumor cell line can be suppressed by transfection with E-cadherin, and invasiveness can be restored by anti-E-cadherin antibodies [86]. Loss of E-cadherin expression in HNSCC has been found to correlate with both the extent of dedifferentiation of the tumor and, more importantly, with the probability of lymph node metastasis [87-89]. The mechanism of E-cadherin inactivation in HNSCC is not known.
Matrix metalloproteinases — The matrix metalloproteinases (MMPs), a family of secreted enzymes that degrade extracellular matrix proteins, have been implicated in the normal processes of tissue regeneration and remodeling. Expression of certain members of the MMP family, including MMP-2, MMP-9, and MMP-13, has been associated with increased local invasion, high metastatic potential, and poor clinical outcome in HNSCC [90-92]. In addition, the expression of a natural inhibitor of MMPs, TIMP-1, also appears to have prognostic significance in patients with HNSCC [93,94]. Tumor expression of MMPs may be an important determinant of tumor growth, spread, and clinical outcome.
A prospective study from Johns Hopkins collected tumor samples from 124 patients with HNSCC and evaluated for promoter hypermethylation for TIMP-3 and DAPK using a quantitative methylation-specific polymerase chain reaction (qMSP) [95]. TIMP-3 is a known tumor suppressor gene on chromosome 12q 12.3 and is part of a family of genes that inhibit MMPs. TIMP-3 regulates processes including invasion, migration, differentiation, and proliferation. DAPK is a serine-threonine kinase found to be an integral part of the interferon-induced apoptotic pathway. TIMP-3 was hypermethylated in 71.8 percent of the tumor samples, and DAPK was hypermethylated in 74.2 percent, both significantly higher than in control specimens. There was a strong correlation for hypermethylation between the two genes. The roles of these genes in HNSCC tumorigenesis are being actively studied.
MMPs represent a potential therapeutic target. Although initial clinical trials with small-molecule MMP inhibitors in advanced solid tumors have been disappointing, evaluation in patients with very early stage disease (in which these agents might be predicted to be of greatest potential efficacy) has not been undertaken [96].
DISRUPTION OF CELL DEATH PATHWAYS — Inhibition of programmed cell death (apoptosis) pathways by either cellular or viral mechanisms is a characteristic feature of many human cancers [97]. Overexpression of transforming oncogenes, in the absence of apoptotic inhibition, efficiently triggers programmed cell death in many contexts, including cultured epithelial cells [98,99]. These observations suggest that apoptotic dysregulation may be a critical event in the process of carcinogenesis.
Among the many other factors known to regulate apoptotic pathways are the B cell leukemia/lymphoma 2 (Bcl-2) family members. This family consists of both proapoptotic and antiapoptotic members that form heterodimers that determine apoptotic threshold [100]. Approximately 70 percent of HNSCCs demonstrate upregulated expression of one of two antiapoptotic genes in this family, Bcl-xL and Bcl-2 [101].
Multiple studies have found an association between Bcl-2 overexpression and better clinical outcome, including response to chemotherapy, local control, time to progression, and survival [101-103]. This finding is surprising since apoptotic inhibition by factors such as Bcl-2 confers both chemotherapeutic and radiation resistance in cell lines [15] and might be expected to promote viability of micrometastases, resulting in a highly resistant and rapidly spreading cancer. Although a similar paradoxical finding has been noted in other solid tumors, the basis for this association has not been determined.
IMMUNE LANDSCAPE AND PD-1/PD-L1 PATHWAY IN HNSCC — The human papillomavirus (HPV) associated head and neck squamous cell carcinoma (HNSCC) arises from deep crypts within the tonsillar and base of tongue lymphoid tissue, characterized by infiltration of lymphocytes in the stroma and tumor nests [104]. Despite this lymphocytic infiltration of tumor tissue, the HPV associated tumors are able to evade the immune system and proliferate. This may be related to dysregulation of antigen-induced activation and overexpression of co-inhibitory receptors/ligands on the tumor cell surface/lymphocytes, such as programmed cell death protein 1 (PD-1) and programmed cell death ligand 1 (PD-L1), referred to as immune checkpoints. Most studies suggest a positive correlation between PD-L1 expression and HPV positivity [105]. Checkpoint inhibitors specifically targeting PD-1 and PDL1 have significant clinical activity in patients with metastatic HNSCC. (See "Treatment of metastatic and recurrent head and neck cancer", section on 'PD-1 inhibitor immunotherapy'.)
Overexpression of PD-L1 in tumor cells commonly results from induction of cytokines, such as interferon (IFN)-gamma secreted by the immune cells, as well as intrinsic mechanisms. The PI3K pathway has been implicated in PD-L1 expression in oral cavity cancer. IFN-gamma was shown to induce PD-L1 expression by upregulation of protein kinase D isoform 2, a downstream target of PI3K [106,107]. Furthermore, inactivation of PTEN has been observed to be associated with increased PD-L1 expression [108].
The prognostic value of PD-1/PD-L1 expression in HNSCC remains controversial. Some studies suggest that PD-L1 expression is associated with tumor size, clinical stage, regional and distant metastases, and worse overall survival [109,110]. Other studies suggest that higher PD-1/PD-L1 expression correlated with fewer local and distant recurrences, especially in those with HPV associated disease [111]. Yet other studies found that PD-L1 expression did not correlate with prognosis in HNSCC [111]. As an example, one meta-analysis did not detect a difference in survival between patients with PD-L1-positive and PD-L1-negative tumors [112].
Alternately, PD-L1 expression on immune cells rather than tumor cells may carry predictive value. A combined positive score (CPS), which takes into account PD-L1 expression on lymphocytes, macrophages, and tumor cells, is used to guide therapy in HNSCC [112,113]. Further details on the use of CPS score and immunotherapy in advanced and metastatic head and neck cancer are discussed separately. (See "Treatment of metastatic and recurrent head and neck cancer".)
Our understanding of the role of immune infiltration, activation, and immunoregulatory influence in HNSCC is evolving. Clinical trials are needed to determine whether information about the tumor immune microenvironment should inform therapy decisions. The following studies provide insight into the immune landscape of HNSCC.
An analysis of 280 HNSCC tumors previously profiled by The Cancer Genome Atlas (TCGA) found that HNSCC is one of the highly immune-infiltrated and immune-regulated cancer types [114]. Immune infiltration differed by tumor subsite, HPV status, and tobacco smoking:
●Tumor subsite – Tumors arising in the oropharynx had higher levels of T cell infiltration, with higher levels of immunoregulatory influence manifested by a lower CD8+/Treg ratio compared with oral cavity, hypopharynx, and larynx subsites.
●Human papillomavirus status – HPV associated tumors contained higher levels of infiltrating Tregs and CD8+ T cells, and higher expression of the immuno-inhibitory receptor cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) compared with non-HPV associated HNSCC. PD-1 and PD-L1 expression was comparable in HPV associated and non-HPV associated tumors. Compared with other highly immune-infiltrated cancer types, the HPV associated and non-HPV associated HNSCC tumors had the highest levels of infiltration with CD56dim NK cells. CD56dim NK cells are inhibited by killer cell immunoglobulin-like receptors (KIR), and KIR gene expression was higher in HPV associated tumors.
●Tobacco smoking – HNSCC with a genetic smoking signature (high mutational loads) had low levels of immune infiltration and correlated with poor survival, offering a potential explanation for the known association between tobacco smoking and inferior prognosis in patients with HPV associated HNSCC [115-117].
Another study of 522 HNSCC tumors from TCGA analyzed the immune pathway-related gene expression profile using RNA sequencing [118]. Significant enrichment of immune cells (T cell, B cell, macrophages), immune-related patterns of gene expression (T/NK and B/P metagenes), and interferon alpha gene signatures were identified in 40 percent of HNSCC tumors (termed "immune class tumors"). These "immune class tumors" had better overall survival than "non-immune class tumors." Immune class tumors could be subdivided based on the absence ("active immune class") or presence ("exhausted immune class") of activated stroma in the tumor microenvironment:
●The "active immune class" was characterized by B cell-related immune signatures, cytolytic activity, and proinflammatory M1 macrophages, suggesting that the humoral immune response could influence intratumoral immune response activation and exhaustion.
●The "exhausted immune class" was characterized by antiinflammatory M2 macrophages, activated stroma, and other tumor-promoting signals, such as the WNT/transforming growth factor (TGF)-beta signaling pathway, suggesting that these could suppress host immune response.
The "active immune class" profile was associated with superior prognosis and was seen more commonly in tumors of the oropharynx, those with HPV infection identified by p16 immunohistochemistry/HPV in situ hybridization, and early pathologic T stage.
Further studies are needed to determine whether tumor immune class might be used to tailor treatment strategies. One hypothesis is that the "active immune class" may be more likely to respond to single-agent checkpoint inhibitors, whereas the "exhausted immune class" may need a combination of treatments (eg, a checkpoint inhibitor plus a TGF-beta inhibitor), and the "non-immune class" may require a combination that would attract T cell infiltration into the tumor microenvironment (eg, a combination of anti-CTLA-4 and anti-PD-1/PD-L1 therapy) [118].
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Head and neck cancer".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topics (see "Patient education: Throat cancer (The Basics)" and "Patient education: Tongue cancer (The Basics)" and "Patient education: Laryngeal cancer (The Basics)")
SUMMARY
●Our molecular understanding is rapidly progressing regarding the development of head and neck squamous cell carcinoma (HNSCC) as well as the influence of the immune landscape in this disease. Data reiterate the complexity of carcinogenic transformation noted in other solid tumor models.
Molecular analysis of the p53 gene mutations and increased mutational load in smokers versus nonsmokers solidified the causal relationship between carcinogens in tobacco and HNSCC. (See 'Introduction' above.)
●The genetic alterations associated with progressive stages of carcinogenic transformation and a better understanding of the immune infiltration, activation, and regulation in development of HNSCC may be relevant to the success of chemopreventive strategies in addition to histologic analysis. (See 'Genomic alterations and multistep carcinogenesis' above and "Chemoprevention and screening in oral dysplasia and squamous cell head and neck cancer".)
●Many of the molecular defects identified in the above studies have yielded new targets that may result in novel therapeutic approaches in HNSCC and other cancers. Strategies have been developed to target cells with aberrant expression of epidermal growth factor (EGF), human epidermal growth factor 2 (HER2), HRAS, B cell leukemia/lymphoma 2 (Bcl-2), p53, p16, and PI3K, among others. Strategies to address epidermal growth factor receptor (EGFR) resistance by targeting alternative downstream signals (such as src) are the focus of ongoing trials. (See 'Disruption of mitogenic signaling pathways' above.)
●The association of HNSCC with oncogenic human papillomavirus (HPV) is a risk factor for developing oropharyngeal cancer. HPV associated tumors have a better prognosis than do those that are not HPV associated, and treatment may evolve to account for HPV status. (See 'Disruption of cell cycle control' above and 'Human papillomavirus' above.)
●HPV associated and non-HPV associated HNSCC are among the highly immune-infiltrated cancer types with immunoregulatory influence poised to benefit from approaches that target immunoregulation with immune checkpoint inhibitors. (See 'Immune landscape and PD-1/PD-L1 pathway in HNSCC' above.)
●Our understanding of the role of immune infiltration, activation, and immunoregulatory influence in HNSCC is evolving. RNA profiling to identify "active immune class," "exhausted immune class," and "non-immune class" subgroups in HNSCC could play a role in tailoring and optimizing immunotherapeutic strategies for future clinical trials. (See 'Immune landscape and PD-1/PD-L1 pathway in HNSCC' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Shanthi Marur, MD, MBBS, who contributed to an earlier version of this topic review.
آیا می خواهید مدیلیب را به صفحه اصلی خود اضافه کنید؟
