Merkel Cell Polyomavirus-Negative Merkel Cell Carcinoma Presenting in the Parotid Gland: Precise Diagnosis and Complete Pathological Response to Nivolumab.
4 affiliations
- 1Wake Forest University School of Medicine, Winston-Salem, NC, U.S.A.
- 2Department of Otolaryngology-Head and Neck Surgery, Kaiser Permanente Roseville Medical Center, Roseville, CA, U.S.A.
- 3Department of Otolaryngology-Head and Neck Surgery, Kaiser Permanente South Sacramento Medical Center, Sacramento, CA, U.S.A.
- 4Department of Pathology and Laboratory Medicine, Kaiser Permanente Sacramento Medical Center, Sacramento, CA, U.S.A.
Abstract
Background/aim
Merkel cell carcinoma (MCC) is a rare and aggressive cutaneous neuroendocrine carcinoma that may present diagnostic challenges, particularly in Merkel cell polyomavirus (MCPyV)-negative cases. Distinguishing MCC from other high-grade neuroendocrine carcinomas is critical because treatment strategies differ.Case report
We report a case of a 77-year-old Caucasian male with a history of multiple non-melanoma skin cancers who presented with rapidly enlarging left parotid and cervical lymph node masses with suspected osseous metastasis to the fourth cervical vertebra (C4). Fine needle aspiration of the parotid mass demonstrated high-grade neuroendocrine carcinoma, positive for synaptophysin, focally and weakly positive for cytokeratin 20 (CK20), and negative for thyroid transcription factor 1 (TTF-1) and Merkel cell polyomavirus (MCPyV) immunoreactivity. Initial molecular classification favored small cell carcinoma. However, additional mutational signature analysis demonstrated an ultraviolet (UV) mutational profile consistent with cutaneous origin, supporting MCPyV-negative Merkel cell carcinoma. The diagnosis was revised following multidisciplinary review, and planned treatment was changed from carboplatin-etoposide chemotherapy to three months of nivolumab, a programmed death-1 (PD-1) inhibitor. Surgical resection of the parotid gland demonstrated complete pathologic response with no residual viable carcinoma identified. At the two-year follow-up, the patient was doing well with no MCC recurrence or metastasis identified.Conclusion
This case highlights the diagnostic difficulty of MCPyV-negative MCC presenting in an extracutaneous location and mimicking small cell carcinoma. In diagnostically challenging MCCs, molecular profiling and UV mutational signature analysis may play a key role in establishing correct diagnosis and treatment.
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BibTeX
@article{li2026merkel,
title = {{Merkel Cell Polyomavirus-Negative Merkel Cell Carcinoma Presenting in the Parotid Gland: Precise Diagnosis and Complete Pathological Response to Nivolumab.}},
author = {Arthur Z Li and Daniel I Chung and Shannon M Poti and Thomas R O'Toole and Jinping Lai},
journal = {Cancer diagnosis \& prognosis},
year = {2026},
month = nov,
doi = {10.21873/cdp.10607},
url = {https://europepmc.org/article/MED/42968934},
note = {CC BY-NC-ND},
}
RIS
TY - JOUR
TI - Merkel Cell Polyomavirus-Negative Merkel Cell Carcinoma Presenting in the Parotid Gland: Precise Diagnosis and Complete Pathological Response to Nivolumab.
AU - Arthur Z Li
AU - Daniel I Chung
AU - Shannon M Poti
AU - Thomas R O'Toole
AU - Jinping Lai
PY - 2026
DA - 2026/11/01
JO - Cancer diagnosis & prognosis
DO - 10.21873/cdp.10607
UR - https://europepmc.org/article/MED/42968934
AB - Background/aim Merkel cell carcinoma (MCC) is a rare and aggressive cutaneous neuroendocrine carcinoma that may present diagnostic challenges, particularly in Merkel cell polyomavirus (MCPyV)-negative cases. Distinguishing MCC from other high-grade neuroendocrine carcinomas is critical because treatment strategies differ.Case report We report a case of a 77-year-old Caucasian male with a history of multiple non-melanoma skin cancers who presented with rapidly enlarging left parotid and cervical lymph node masses with suspected osseous metastasis to the fourth cervical vertebra (C4). Fine needle aspiration of the parotid mass demonstrated high-grade neuroendocrine carcinoma, positive for synaptophysin, focally and weakly positive for cytokeratin 20 (CK20), and negative for thyroid transcription factor 1 (TTF-1) and Merkel cell polyomavirus (MCPyV) immunoreactivity. Initial molecular classification favored small cell carcinoma. However, additional mutational signature analysis demonstrated an ultraviolet (UV) mutational profile consistent with cutaneous origin, supporting MCPyV-negative Merkel cell carcinoma. The diagnosis was revised following multidisciplinary review, and planned treatment was changed from carboplatin-etoposide chemotherapy to three months of nivolumab, a programmed death-1 (PD-1) inhibitor. Surgical resection of the parotid gland demonstrated complete pathologic response with no residual viable carcinoma identified. At the two-year follow-up, the patient was doing well with no MCC recurrence or metastasis identified.Conclusion This case highlights the diagnostic difficulty of MCPyV-negative MCC presenting in an extracutaneous location and mimicking small cell carcinoma. In diagnostically challenging MCCs, molecular profiling and UV mutational signature analysis may play a key role in establishing correct diagnosis and treatment.
SN - 2732-7787
ER -