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We previously studied the genetic and immunohistochemical profiles of subsets of Merkel cell carcinoma (MCC) stratified by morphology and Merkel cell polyomavirus (MCPyV) status. Recent advances in the immunotherapy of this disease prompted us to examine markers of immunogenicity [PD-L1 expression and tumor-infiltrating lymphocytes (TILS) in these subsets]. The observed clinical responses to checkpoint inhibition of the PD-1/PD-L1 pathway have not correlated with PD-L1 expression by MCC cells, and recent evidence suggests that functions of this pathway within the immune tumor microenvironment may be relevant. We conducted a semiquantitative (high, moderate, and minimal) immunohistochemical evaluation of the global PD-L1 signal in 52 cases of MCC, segregated in 3 subsets [pure MCPyV-positive (n = 28), pure MCPyV-negative (n = 9), and combined MCPyV-negative (n = 15)]. TILS were categorized as brisk, nonbrisk, or absent. Intersubset comparisons revealed that high global PD-L1 signals were exclusively associated with pure MCPyV-positive MCCs contrasted with virus-negative cases (P = 0.0003). Moderate signals were seen across all 3 groups. Brisk TILS were significantly associated with MCPyV-positive MCCs compared with MCPyV-negative cases (P = 0.029). Neither parameter (PD-L1 or TILS) was significantly different between the MCPyV-negative groups. Of potential clinical relevance, MCPyV seems to convey greater immunogenicity to MCCs than the high mutational burden/greater neoantigen load of MCPyV-negative cases. Interesting too is the fact that subset-related profiles of these markers mirrored those noted at genetic and immunohistochemical levels, separating pure MCPyV-positive MCCs from the virus-negative subsets.

A healthy 50-year-old woman had a tattoo performed on the posterior aspect of her neck and another on the dorsum of her left foot. Several weeks later, she noted redness, tenderness, and intense pruritis at both tattoo sites. Treatment with cephalexin and hydrocortisone cream was instituted, without success. Within a few months, the red, but not black, pigment had disappeared from both tattoos and was replaced by pale areas of scarring. Persistently enlarged left supraclavicular and suboccipital lymph nodes were excised 7 and 10 months after receipt of the tattoos, respectively. The nodes were pigmented on gross examination, and on microscopy, a granuloma annulare-like reaction was observed. Normal lymphoid tissue was seen to be replaced by large palisading granulomas with central degenerative change, abundant stromal mucin, and scattered deposits of tattoo pigment. Histochemical stains, tissue culture, and serological studies revealed no evidence of infection. There are rare reports of granuloma annulare-like reactions in tattoos, and these are believed to represent delayed-type hypersensitivity reactions. Our case is unique in the observation of this reaction pattern in regional lymph nodes, and it expands the spectrum of complications known to be associated with tattoos.