Immunotherapy Treatment for Head and Neck Cancer

Immunotherapy has reshaped how advanced head and neck cancer is treated, with checkpoint inhibitor drugs now serving as the standard of care for recurrent or metastatic disease. The U.S. FDA approved pembrolizumab and nivolumab for head and neck squamous cell carcinoma (HNSCC) in 2016, and subsequent trials moved pembrolizumab into the first-line setting, where it extended survival compared to the previous chemotherapy-plus-cetuximab standard. But the drugs do not work equally well for everyone, and a substantial share of patients still see their tumors progress. How oncologists identify who will benefit, what newer strategies are in development, and what the real-world experience looks like are questions that matter as much as the headline approvals.

How Checkpoint Inhibitors Reached Head and Neck Cancer

Head and neck squamous cell carcinoma was long treated with surgery, radiation, and platinum-based chemotherapy. Cetuximab, an antibody targeting the epidermal growth factor receptor, became the first major new drug approved for HNSCC in 2006, after a three-decade gap in systemic therapy advances.¹ A decade later, the field shifted dramatically. Pembrolizumab and nivolumab, both antibodies that block the PD-1 receptor on immune cells, received FDA approval in 2016 for patients whose tumors had progressed after platinum chemotherapy.² The rationale is straightforward: many HNSCC tumors express PD-L1, a protein that essentially tells approaching T cells to stand down. Blocking PD-1 on those T cells removes the brake, allowing the immune system to recognize and attack the tumor.

What made researchers confident this would work in head and neck cancer specifically was the observation that these tumors are often heavily infiltrated by immune cells that appear ready to fight but are being suppressed. Studies of HPV-positive HNSCC tumors found that a large majority of the CD8-positive T cells surrounding tumors expressed PD-1, with one analysis reporting a mean frequency above 70 percent.³ Those T cells were right there at the tumor’s edge, held in check by PD-L1 expressed on both cancer cells and immune cells called tumor-associated macrophages. Releasing that brake offered an obvious therapeutic opportunity.

First-Line Treatment and the KEYNOTE-048 Trial

The study that changed the treatment landscape for recurrent or metastatic HNSCC was KEYNOTE-048, a large phase III trial comparing pembrolizumab (alone or with chemotherapy) against the existing standard of cetuximab plus chemotherapy. Updated results showed that pembrolizumab combined with chemotherapy improved overall survival across all comers, with a hazard ratio of 0.71 in the total population. For patients whose tumors had higher PD-L1 expression, the benefit was more pronounced: in the group with a combined positive score (CPS) of 20 or above, the hazard ratio dropped to 0.62, meaning the risk of death was reduced by roughly 38 percent compared to the older regimen.⁴

These results established pembrolizumab, either alone or with platinum-based chemotherapy, as the new first-line standard for recurrent or metastatic HNSCC. Pembrolizumab alone was shown to be noninferior to the cetuximab regimen even in the total study population, and it was superior in the PD-L1-enriched subgroups. One of the trial’s practical contributions was establishing the CPS threshold: oncologists now routinely test tumors for PD-L1 expression to guide treatment decisions, with scores of 1 and 20 serving as key cutoffs.

Second-Line Treatment After Platinum Failure

For patients whose disease progresses after platinum-based chemotherapy, nivolumab was the first checkpoint inhibitor to demonstrate a survival advantage in a randomized trial. The CheckMate 141 study compared nivolumab to the physician’s choice of standard therapy (methotrexate, docetaxel, or cetuximab) and found that median overall survival was 7.5 months with nivolumab versus 5.1 months with standard treatment. The one-year survival rate was roughly 36 percent with nivolumab compared to about 17 percent with standard therapy.⁵

That 19-percentage-point gap in one-year survival was meaningful, but it also revealed a hard truth: most patients still did not respond. Early data from the KEYNOTE-012 trial of pembrolizumab in the platinum-refractory setting showed an overall response rate of about 18 percent, with responses tending to be durable when they occurred. Among responders, most responses lasted at least six months, and roughly two-thirds were still ongoing at data cutoff.⁶ The pattern is characteristic of immunotherapy broadly: a minority of patients get substantial, sometimes lasting benefit, while the majority does not respond at all. Figuring out who falls into which category remains one of the field’s central challenges.

Why HPV Status Matters

Human papillomavirus (HPV) causes a growing proportion of oropharyngeal cancers, and these HPV-positive tumors behave differently from HPV-negative ones in almost every respect, including how they interact with the immune system. HPV-positive head and neck cancers tend to be more heavily infiltrated by immune cells, particularly CD8-positive T cells, natural killer cells, and B cells.⁷ They also show greater T-cell receptor diversity, suggesting the immune system is recognizing a wider array of tumor targets.

This difference in immune environment translates to a measurably different response to immunotherapy. In the KEYNOTE-012 pooled analysis, the response rate to pembrolizumab was about 24 percent in HPV-associated disease compared to 16 percent in non-HPV-associated disease.⁶ Intriguingly, HPV-positive tumors also express higher levels of T-cell exhaustion markers like PD-1, LAG3, and TIGIT. This seems paradoxical, but patients whose tumors showed more of these exhaustion markers actually had markedly improved survival when the cancer was HPV-positive, while the same pattern did not predict better outcomes in HPV-negative disease.⁸ The exhaustion markers, in other words, are signs of an immune system that has been actively fighting and can potentially be reinvigorated.

HPV-positive tumors also show increased expression of B-cell-related genes and greater B-cell density within the tumor, suggesting that the humoral immune response contributes to the inflammatory environment alongside T cells.⁹ Taken together, HPV-positive HNSCC looks like a more “immunotherapy-ready” cancer, though HPV-negative tumors can still respond, and HPV status alone is not the deciding factor in treatment selection.

PD-L1 Scoring and Other Biomarkers

The most widely used biomarker for predicting who will benefit from checkpoint inhibitors is PD-L1 expression, measured by staining tumor tissue. Two scoring systems are common: the tumor proportion score (TPS), which counts only tumor cells expressing PD-L1, and the combined positive score (CPS), which also counts immune cells in the sample. In practice, both scoring methods perform similarly for predicting pembrolizumab benefit. One analysis comparing the two approaches found that patients with TPS of 50 percent or above who received pembrolizumab had a median overall survival of about 11.4 months versus 6.6 months on standard therapy, and CPS at the same threshold yielded nearly identical survival curves.¹⁰

A CPS of 50 appears to be a particularly important threshold. A study of patients receiving anti-PD-1 monotherapy found that progression-free survival was significantly better in the CPS-50-and-above group (median 8.4 months versus 3.2 months), while lower cutoffs of 1 or 20 did not produce a clear separation in outcomes.¹¹ Patients with virtually no PD-L1 expression (TPS below 1 percent) had notably poor outcomes on immunotherapy alone.

PD-L1 scoring is useful but imperfect. Researchers have found that additional biomarkers add predictive value. Tumor mutational burden, a measure of how many mutations a tumor carries, and a T-cell-inflamed gene expression profile, which captures how actively the immune system is engaging the tumor, were both significantly associated with response to pembrolizumab in one analysis of HNSCC patients.¹² Adding PD-L2 expression to the scoring model may further improve prediction of who benefits from nivolumab.¹³ The field is moving toward multi-biomarker panels rather than relying on any single test.

Quality of Life on Immunotherapy

A common concern for patients is whether immunotherapy trades survival gains for worsened daily life. The KEYNOTE-048 trial tracked health-related quality of life using validated questionnaires measuring overall well-being, pain, and swallowing, all of which are critical for people with head and neck cancer. Quality-of-life scores remained stable through 15 weeks across all treatment arms, with no clinically meaningful differences between pembrolizumab-based regimens and the cetuximab-chemotherapy control. Time to deterioration in overall quality of life, pain, and swallowing was similar across groups and was not reached over 51 weeks of follow-up.¹⁴

This is reassuring because the side-effect profile of checkpoint inhibitors is genuinely different from that of traditional chemotherapy. Rather than the typical nausea, hair loss, and bone marrow suppression, immunotherapy can trigger autoimmune-like reactions where the unleashed immune system attacks healthy tissues. Thyroid inflammation, skin rashes, colitis, and liver inflammation are among the more common immune-related adverse events. These are usually manageable with steroids or treatment pauses, but serious events do occur and require close monitoring. The Society for Immunotherapy of Cancer has published consensus guidelines for managing these adverse events specifically in HNSCC patients.¹⁵

Immunotherapy Before Surgery

An increasingly active area of research is giving immunotherapy before surgery, known as the neoadjuvant setting. The idea is that checkpoint inhibitors, given while the bulk of the tumor is still present, can prime a stronger and broader immune response than when given after the tumor has been removed. Early trials have produced eye-catching results: one study combining immunotherapy with radiation before surgery reported a complete pathological response rate of 67 percent and clinical-to-pathological downstaging in 90 percent of patients.¹⁶

A systematic review and meta-analysis across multiple neoadjuvant trials painted a more tempered picture. The complete pathological response rate for immunotherapy agents alone (without concurrent radiation) was low overall, around 4 percent, though the partial response rate reached 58 percent with the nivolumab-plus-ipilimumab combination. Disease progression after surgery was lowest in the dual-immunotherapy group, at roughly 8 percent.¹⁷ The gap between the single-study results and the pooled data highlights how early this field is: the most promising protocols combine immunotherapy with radiation or dual checkpoint blockade, and larger confirmatory trials are still needed.

Why Some Tumors Resist Immunotherapy

The tumor microenvironment in head and neck cancer can be profoundly immunosuppressive, and understanding why is key to improving response rates. Several cell types conspire to shield the tumor from immune attack. Regulatory T cells dampen the activity of effector T cells. Myeloid-derived suppressor cells accumulate in the tumor and surrounding tissue. Tumor-associated macrophages, as noted earlier in the context of PD-L1 expression, can form a physical and biochemical barrier around tumor nests.³

Beyond cellular players, signaling molecules further tilt the environment against immune activity. TGF-beta signaling, for instance, has been identified through single-cell analyses as a driver of interactions between cancer-associated fibroblasts and a subset of mesenchymal cancer cells, promoting invasiveness, treatment resistance, and immune evasion.¹⁸ These layered mechanisms of resistance explain why blocking PD-1 alone is insufficient for most patients and why combination strategies are an intense area of research.

Combination Strategies and Emerging Approaches

One promising combination pairs checkpoint inhibitors with cetuximab, the older EGFR-targeting antibody. A phase II trial of pembrolizumab plus cetuximab in recurrent or metastatic HNSCC reported a response rate of 45 percent at six months, substantially higher than what either agent typically achieves alone.¹⁹ Combining immunotherapy with radiation is another active frontier, since radiation can trigger immunogenic cell death that releases tumor antigens and potentially amplifies the immune response initiated by checkpoint blockade.

Oncolytic viruses represent a more unconventional approach. These are engineered viruses that selectively infect and kill cancer cells while alerting the immune system to the tumor’s presence. Talimogene laherparepvec (T-VEC), approved for advanced melanoma, has shown safety and antitumor activity in head and neck cancer, and preclinical work suggests it may synergize with pembrolizumab by converting immunologically “cold” tumors into “hot” ones that checkpoint inhibitors can then target.²⁰

Therapeutic vaccines targeting HPV proteins are also being tested, particularly for HPV-driven oropharyngeal cancers. These vaccines aim to boost T-cell responses against the E6 and E7 viral proteins that HPV-positive cancer cells depend on. Multiple platforms are in early-phase trials, including peptide vaccines, DNA and mRNA vaccines, and viral-vector-based approaches. When combined with checkpoint inhibitors, some have shown encouraging immune activation, though clinical efficacy data is still preliminary.²¹

CAR-T Cells and the Solid Tumor Challenge

Chimeric antigen receptor T-cell (CAR-T) therapy has transformed the treatment of certain blood cancers, but adapting it to solid tumors like HNSCC has proven far more difficult. The obstacles are numerous: solid tumors present a hostile microenvironment that suppresses infused T cells, the target proteins on cancer cells vary from cell to cell within the same tumor, and getting CAR-T cells to physically penetrate solid tissue is harder than reaching cancer cells circulating in the bloodstream.²²

Researchers have identified several potential targets on HNSCC cells, including EGFR, HER2, B7-H3, and MUC1, and are engineering more sophisticated CAR-T constructs designed to overcome resistance. Dual-targeted cells that recognize two antigens simultaneously, “armored” CARs that secrete immune-stimulating molecules, and CRISPR-edited T cells with deleted inhibitory genes are all in development.²³ These remain early-stage efforts, and no CAR-T therapy is currently approved or near approval for head and neck cancer.

Activating the Innate Immune System

Most current immunotherapies focus on the adaptive immune system, particularly T cells. But an entirely different arm of the immune system, the innate response, is drawing attention. The STING pathway, a cellular alarm system that detects abnormal DNA and triggers inflammation, is one of the most active research targets. In preclinical HNSCC models, activating STING promoted T-cell infiltration into tumors and generated long-term immune memory against the cancer.²⁴

One challenge is that many HNSCC cells express very low levels of STING, making them unresponsive to agonist drugs. Recent work has shown that inhibiting a specific phosphatase called PTPN2 can restore STING expression across multiple HNSCC cell lines, potentially making previously resistant tumors sensitive to STING-based therapies.²⁵ Combining STING activation with PTPN2 inhibition is still preclinical, but it illustrates the kind of multi-layered strategy that may eventually reach patients who do not respond to PD-1 blockade alone.

The Gut Microbiome and Immunotherapy Response

An unexpected factor influencing immunotherapy outcomes is the composition of bacteria in the gut. In other cancers, particularly melanoma, certain gut bacteria have been linked to better checkpoint inhibitor responses. Research in head and neck cancer is now catching up. A recent study found that patients who responded to anti-PD-1 therapy had an enrichment of a bacterium called Eggerthella lenta in their stool, and its presence correlated with greater CD8 T-cell activation within tumors. In mouse models, oral administration of E. lenta combined with anti-PD-1 therapy produced significantly greater tumor regression than either treatment alone, with higher levels of tumor-infiltrating T cells and increased markers of immune activation.²⁶

The broader picture is that the oral and gut microbiomes appear to influence not just immunotherapy efficacy but also side effects from multiple treatment modalities. Interventions like probiotics, prebiotics, and even fecal microbiota transplantation are being explored as ways to improve treatment outcomes and reduce toxicity.²⁷ None of these are ready for routine clinical use, but they represent a shift in thinking about cancer treatment as something that involves the whole body’s ecosystem, not just the tumor.

Access and Affordability Across the Globe

The scientific progress in immunotherapy collides with a stark economic reality: these drugs are expensive, and access is deeply unequal. An analysis of immunotherapy affordability found that a six-month course of pembrolizumab represented nearly 8,000 percent of average monthly income in India, over 4,300 percent in Pakistan, and about 3,100 percent in Bangladesh. Even in high-income countries, costs exceeded catastrophic thresholds, reaching roughly 590 percent of monthly income in the United States and 900 percent in the United Kingdom.²⁸

Beyond cost, access disparities play out along racial and socioeconomic lines. Research using large cancer databases has found that racial minorities and socioeconomically disadvantaged populations have both lower rates of receiving immunotherapy and worse survival outcomes, pointing to systemic barriers that extend well beyond the price tag of the drugs themselves.²⁹ For a treatment that has genuine potential to extend life, the gap between who could benefit and who actually receives it is one of the most pressing problems in the field.