The emergence of long-term survivors in recurrent and metastatic squamous cell head and neck cancer

Exploring the frontiers: tumor immune microenvironment and immunotherapy in head and neck squamous cell carcinoma

The global prevalence of head and neck malignancies positions them as the sixth most common form of cancer, with the head and neck squamous cell carcinoma (HNSCC) representing the predominant histological subtype. Despite advancements in multidisciplinary approaches and molecular targeted therapies, the therapeutic outcomes for HNSCC have only marginally improved, particularly in cases of recurrent or metastatic HNSCC (R/MHNSCC). This situation underscores the critical necessity for the development of innovative therapeutic strategies. Such strategies are essential not only to enhance the efficacy of HNSCC treatment but also to minimize the incidence of associated complications, thus improving overall patient prognosis. Cancer immunotherapy represents a cutting-edge cancer treatment that leverages the immune system for targeting and destroying cancer cells. It's applied to multiple cancers, including melanoma and lung cancer, offering precision, adaptability, and the potential for long-lasting remission through immune memory. It is observed that while HNSCC patients responsive to immunotherapy often experience prolonged therapeutic benefits, only a limited subset demonstrates such responsiveness. Additionally, significant clinical challenges remain, including the development of resistance to immunotherapy. The biological characteristics, dynamic inhibitory changes, and heterogeneity of the tumor microenvironment (TME) in HNSCC play critical roles in its pathogenesis, immune evasion, and therapeutic resistance. This review aims to elucidate the functions and mechanisms of anti-tumor immune cells and extracellular components within the HNSCC TME. It also introduces several immunosuppressive agents commonly utilized in HNSCC immunotherapy, examines factors influencing the effectiveness of these treatments, and provides a comprehensive summary of immunotherapeutic strategies relevant to HNSCC.

The let-7 family of microRNAs suppresses immune evasion in head and neck squamous cell carcinoma by promoting PD-L1 degradation

Background

Accumulation of immunosuppressive protein programmed death-ligand 1 (PD-L1) has been documented in several cancers and contributes to the evasion of the host immune system. However, cancer cell-intrinsic signaling-dependent control of PD-L1 expression remains to be elucidated. Herein, we aimed to identify the let-7 family of microRNAs as candidates that up-regulate tumor cell PD-L1 expression and mediates immune evasion of head and neck squamous cell carcinoma (HNSCC).

Methods

The expression of let-7 family and PD-L1 was quantified in HNSCC tissues and adjacent normal tissues. PD-L1 degradation was evaluated in HNSCC cells in response to elevated expressions of let-7a or let-7b. The regulation of let-7 family on PD-L1 degradation through a mechanism involving T-cell factor-4 (TCF-4) control of β-catenin/STT3 pathway was evaluated. Immune recognition of HNSCC in vivo was examined in subcutaneous tumor-bearing C3H mice in the presence of let-7a/b and/or CTLA-4 antibody.

Results

The let-7 family were significantly down-regulated in the context of HNSCC, sharing a negative correlation with PD-L1 expression. Glycosylated PD-L1 was detected in HNSCC cells, which was reduced by let-7a/b over-expression. TCF-4, the target of let-7a/b, activated the β-catenin/STT3 pathway and promoted PD-L1 degradation. In vivo analysis demonstrated that let-7a/b over-expression potentiated anticancer immunotherapy by CTLA-4 blockade.

Conclusions

Taken together, our findings highlight targeting let-7 family as a potential strategy to enhance immune checkpoint therapy for HNSCC.

Approach to the Patient with Recurrent/Metastatic Disease

OPINION STATEMENT

For most of patients with a recurrent/metastatic (R/M) head and neck squamous cell carcinoma (HNSCC), the treatment remains palliative: The main objective is to reduce the symptoms related to the locoregional relapse, prolong life while maintaining quality of life, which is a big challenge. The systemic treatment needs to be adapted to the performance status, comorbidities, and sequelae of patients. For fit patients, the combination of platinum-based chemotherapy and cetuximab (EXTREME) is the standard of care in first-line treatment since 2008, as no other targeted therapy has been approved in this setting until now. The replacement of 5-FU with a taxane (docetaxel) in the EXTREME regimen has been explored in the large randomized international study TPExtreme which results are awaited in a few months. Depending on the study results on survival, response rate, and tolerance, the TPEx regimen may become a treatment option for patients with R/M HNSCC. Unfit patients are usually treated with platinum-free combinations or with the monotherapies which are recommended in second-line setting (methotrexate, taxanes, cetuximab). However, the irruption of new immunotherapies (e.g., checkpoint inhibitors (CPI)) is changing the guidelines. The tolerance of anti-PD-1 CPI is better than that of chemotherapy, and they seem to be a good option for unfit patients. Anti-PD-1 nivolumab and pembrolizumab are now approved for platinum refractory patients, providing prolonged survival in the case of response, and improvement in quality of life. New options arise in first-line setting with pembrolizumab alone or combined with chemotherapy. Patients with a high PD-L1 biomarker level seem to benefit more from immunotherapy. Other situations (e.g., PD-L1-low, PD-L1-negative, high tumor burden) may more likely to benefit from other combinations, such as cetuximab plus chemotherapy, to avoid local failures and life-threatening fast progression. In terms of perspectives, chemo-free and CPI-free approaches, using other immune oncology agents, should be the next steps.