Evaluation of clinical characteristics and pre-biopsy impressions of primary Merkel cell carcinoma of the skin.

Merkel cell carcinoma is an aggressive carcinoma of the skin notable for protean presentation on physical exam. A retrospective cohort of 232 patients with primary cutaneous Merkel cell carcinoma was reviewed for availability of data on pre-biopsy clinical differential diagnosis based on clinical exam. Data was available for 192 patients (83%). The three most common impressions were cyst (33.3%), basal cell carcinoma (31.8%), and squamous cell carcinoma (19.8%). Merkel cell carcinoma was correctly suspected in only 13 cases (6.8%). A greater proportion of lesions that were less than or equal to 2 cm in diameter (10.2%) or carried BCC as a co-diagnosis (11.5%) were correctly suspected as Merkel cell carcinoma prior to biopsy, versus lesions greater than 2 cm in diameter (1.6%) or carrying SCC as a co-diagnosis (2.6%), suggesting that clinicians may be anchoring on the well-publicized concept of Merkel cell carcinoma as a small, pearly papule in real-world practice.

Metastatic Merkel Cell Carcinoma Masquerading as Multiple Immune-Related Adverse Events.

Merkel cell carcinoma is a rare cutaneous neuroendocrine carcinoma with a high rate of regional and distant metastasis and mortality. Here, we report a novel case of Merkel cell carcinoma which presented as a primary lesion to the left cheek with regional lymph node involvement and was treated with pembrolizumab and radiation. Widely metastatic disease eventually revealed on autopsy clinically mimicked immune-related organ insult leading to management with immunosuppressants. The patient also had a biopsy-confirmed immune-related cutaneous adverse event during admission. The case highlights a rare circumstance in which disease progression masqueraded as multiple immune-related end-organ adverse events. Contribution of on-target anti-PD-1 toxicity remains a possibility.