Metastatic Merkel Cell Carcinoma Associated Paraneoplastic Hyponatraemia: Response to Avelumab

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Introduction: Merkel cell carcinoma (MCC) is rare, encompassing primary cutaneous neuroendocrine carcinoma.It has an aggressive natural history, and exhibits high response rates to radiotherapy & chemotherapy but often of short duration.

Aim(s): We report a case of paraneoplastic hyponatraemia occurring with metastatic MCC and literature review.

Materials and methods: 63 year old man presented with a hyperaemic mass on his right thigh Oct. 2015. Biopsy confirmed MCC. CTCAP: No metastatic spread. Surgical resection performed. An involved right inguinal lymph node (LN) was diagnosed 9 months later, treated with inguinal LN dissection. No recurrence on serial imaging. Patient was admitted 4 years after 1st presentation; unwell, palpable subcutaneous lesions, largest in left axilla. Biochemistry showed hyponatraemia (120). Paired urine/serum osmolality indicated SIADH. CT head: no intracranial cause. CTCAP: extensive subcutaneous & peritoneal nodules & bulky retroperitoneal lymphadenopathy. Biopsy of axillary LN showed recurrent MCC. Avelumab is a new targeted agent licenced by NICE was commenced. We report serial biochemical & radiological assessment documenting degree of response.

Conference: 17th Annual ENETSConcerence (2020)

Presenting Author: Demirel S

Authors: Saunders E, Demirel S, Kim S, Skelly R, Mukesh M,

Keywords: merkel cell carcinoma, paraneoplastic syndrome, hyponatraemia,