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Head and neck squamous cell carcinoma (HNSCC) is a heterogeneous disease with significant mortality and frequent recurrence. Prior efforts to transcriptionally classify HNSCC into groups of varying prognoses have identified four accepted molecular subtypes of the disease: Atypical (AT), Basal (BA), Classical (CL), and Mesenchymal (MS). Here, we investigate the active enhancer landscapes of these subtypes using representative HNSCC cell lines and identify samples belonging to the AT subtype as having increased enhancer activity compared to the other 3 HNSCC subtypes. Cell lines belonging to the AT subtype are more resistant to enhancer-blocking bromodomain inhibitors (BETi). Examination of nascent transcripts reveals that both AT TCGA tumors and cell lines express higher levels of enhancer RNA (eRNA) transcripts for enhancers controlling BETi resistance pathways, such as lipid metabolism and MAPK signaling. Additionally, investigation of higher-order chromatin structure suggests more enhancer-promoter (E-P) contacts in the AT subtype, including on genes identified in the eRNA analysis. Consistently, known BETi resistance pathways are upregulated upon exposure to these inhibitors. Together, our results identify that the AT subtype of HNSCC is associated with higher enhancer activity, resistance to enhancer blockade, and increased signaling through pathways that could serve as future targets for sensitizing HNSCC to BET inhibition.

Merkel cell carcinoma has historically had dismal prognosis with limited cytotoxic chemotherapy options that provide durable control of metastatic disease. The advent of anti-programmed death protein (anti-PD1)/anti-programmed death-ligand 1 (anti-PD-L1) directed immunotherapy has shown initial promise in Merkel cell carcinoma and radiation might augment immune responses. We present a case report of a 70-year-old male who underwent resection of Merkel cell carcinoma of the right thigh with a close margin and positive right inguinal involvement. Due to high-risk features, the patient was treated with adjuvant radiation to the right groin and with systemic carboplatin/etoposide, but developed local failure requiring salvage surgical resection. The patient then developed metastatic disease with biopsy proven retroperitoneal involvement refractory to doxorubicin/cyclophosphamide chemotherapy. The patient was then transitioned to single-agent pembrolizumab with a partial response for 10 months until developing progressive disease involving the left inguinal and left external iliac nodal regions. The progressive left inguinal/pelvic disease was treated with conventionally fractionated intensity modulated radiation therapy to a dose of 45 Gy delivered in 25 fractions. Following radiation therapy, the patient had complete response of all sites of disease throughout the body on imaging by RECIST criteria including retroperitoneal and mediastinal disease outside the radiation field. At 20 months post-radiation, the patient remains on pembrolizumab without evidence of disease on imaging. Herein, we present a case of durable response of metastatic Merkel cell carcinoma treated with concurrent radiation and pembrolizumab, providing evidence that radiation might improve systemic responses to anti-PD1/PD-L1 directed immune therapy. Ongoing prospective trials evaluating the utility of radiation in conjunction with immunotherapy for Merkel cell carcinoma are anticipated to provide clarity on the frequency and durability of abscopal responses when radiation is combined with immune checkpoint inhibitors.