Immune‐related adverse events (irAE) were reported to be associated with better outcomes in various cancers treated with the immune checkpoint inhibitor nivolumab. Considering that their development depends on host immune activation, irAE may reflect antitumor response in mucosal melanoma (MM). This single‐center retrospective study including patients with advanced MM receiving nivolumab monotherapy between August 2014 and September 2018 investigated whether the development of irAE was associated with clinical efficacy. The study patients were divided into those with and without irAE, and treatment efficacy and safety were evaluated. The study cohort of 27 patients included 20 (74%), six (22%) and one (4%) patient with primary MM in the head and neck, genitourinary and anorectal regions, respectively. The irAE onset was not significantly associated with the objective response rate in patients while it was significantly associated with the disease control rate. The median progression‐free survival in patients with and without irAE was 301 and 63 days, respectively. The median overall survival (OS) in patients with and without irAE was 723 and 199 days, respectively. According to the timing of irAE onset, the OS was better in seven patients who developed irAE after 180 days than in nine patients who developed irAE within 180 days. Although 16 patients (59%) experienced any grade irAE, including three (11%) with grade 3 or more irAE, there were no treatment‐related deaths. These results indicated that the development of irAE may correlate with improved survival in patients with MM treated with nivolumab monotherapy. Further studies are necessary to confirm these findings.

Distinguishing porocarcinoma from squamous cell carcinoma (SCC) is clinically significant; however, differential diagnosis can often be challenging. This study sought to confirm the diagnostic utility of cytokeratin 19, c-KIT, BerEP4, GATA3, and NUTM1 immunohistochemistry in distinguishing porocarcinoma from SCC. Immunohistochemical analysis of cytokeratin 19, c-KIT, BerEP4, GATA3, and NUTM1 in 14 porocarcinomas and 22 SCCs was performed; the extents and intensities of expression of these markers were recorded. The statistical associations of the immunoexpression between porocarcinoma and SCC were analyzed using the Pearson x 2 test. Cytokeratin 19 was positive in 13 (92.9%) of 14 porocarcinomas, and for all the positive cases, staining was strong and evident in .20% of the tumor cells. By contrast, 9 (40.9%) of 22 SCCs expressed cytokeratin 19 (P = 0.0018), of which 6 showed extremely focal (#10% of the tumor cells) expression. Of the 14 porocarcinomas, 11 (78.6%) cases showed c-KIT positivity, whereas only 3 of 22 SCCs (13.6%) expressed c-KIT focally (P = 0.0001). In addition, BerEP4 immunostaining differed between porocarcinomas and SCCs (57.1% vs. 9.1%, respectively; P = 0.0017). However, no significant difference between the groups was reported in terms of GATA3 expression (57.1% vs. 72.7%, respectively; P = 0.3336). NUTM1 was expressed in 4/14 (28.6%) porocarcinomas but not in the SCCs. Immunohistochemistry for cytokeratin 19, c-KIT, and BerEP4 could be helpful in distinguishing porocarcinomas from SCCs. In addition, NUTM1 immunoexpression is highly specific, although not sensitive, to porocarcinomas. GATA3 immunohistochemistry has no meaningful implications in the differential diagnosis of porocarcinoma and SCC.