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Merkel cell carcinoma (MCC) is a primary neuroendocrine carcinoma of the skin with a 5-year overall survival estimated at 40%.1 In 2008, Merkel cell polyomavirus (MCPyV) integration was identified as the primary oncogenic event of about 80% of MCC cases.1 Under microscopic examination, MCC appears as a proliferation of basaloid tumour cells invading the dermis and subcutaneous tissues.2 Accordingly, MCC belongs to the spectrum of small, round and blue cell proliferations, and differential diagnosis includes haematological malignancies (acute leukaemia and chronic lymphocytic leukaemia), sarcomas and small cell variants of melanoma. Interestingly, positivity of BerEP4 in MCC tumour cells was recently emphasized in the new WHO classification of skin tumours,2 suggesting BerEP4 positivity as a potential pitfall in distinguishing BCC and MCC. Although MCC tumour cells harbour specific cytological features,3 some specimens might be misdiagnosed as BCC especially on small-size biopsies.3 In this specific context, positivity of BerEP4 might constitute a potential diagnostic pitfall. [Extracted from the article]

Background: Histopathological classification of basal cell carcinoma (BCC) has important prognostic and therapeutic implications, but reproducibility of BCC subtyping among dermatopathologists is poor. Objectives: To obtain a consensus paper on BCC classification and subtype definitions. Methods: A panel of 12 recognized dermatopathologists (G12) from nine European countries used a modified Delphi method and evaluated 100 BCC cases uploaded to a website. The strategy involved five steps: (I) agreement on definitions for WHO 2018 BCC subtypes; (II) classification of 100 BCCs using the agreed definitions; (III) discussion on the weak points of the WHO classification and proposal of a new classification with clinical insights; (IV) re‐evaluation of the 100 BCCs using the new classification; and (V) external independent evaluation by 10 experienced dermatopathologists (G10). Results: A simplified classification unifying infiltrating, sclerosing, and micronodular BCCs into a single "infiltrative BCC" subtype improved reproducibility and was practical from a clinical standpoint. Fleiss' κ values increased for all subtypes, and the level of agreement improved from fair to moderate for the nodular and the unified infiltrative BCC groups, respectively. The agreement for basosquamous cell carcinoma remained fair, but κ values increased from 0.276 to 0.342. The results were similar for the G10 group. Delphi consensus was not achieved for the concept of trichoblastic carcinoma. In histopathological reports of BCC displaying multiple subtypes, only the most aggressive subtype should be mentioned, except superficial BCC involving margins. Conclusions: The three BCC subtypes with infiltrative growth pattern, characteristically associated with higher risk of deep involvement (infiltrating, sclerosing, and micronodular), should be unified in a single group. The concise and encompassing term "infiltrative BCCs" can be used for these tumors. A binary classification of BCC into low‐risk and high‐risk subtypes on histopathological grounds alone is questionable; correlation with clinical factors is necessary to determine BCC risk and therapeutic approach. [ABSTRACT FROM AUTHOR]

Hailey-Hailey disease (HHD; MIM 16960), also known as familial benign pemphigus, is a rare autosomal dominant acantholytic genodermatosis, with a prevalence estimated at 1/40 000.[1] HHD is characterized by recurrent grouped vesicles, blisters and erosions restricted almost entirely to the neck and symmetrical intertriginous areas.[2] HHD is caused by mutations in I ATP2C1 i ,[[3]] which encodes an intracellular calcium ATPase pump. Mutations in ATP2C1, encoding a calcium pump, cause Hailey-Hailey disease. Hailey-Hailey disease is caused by mutations in ATP2C1 encoding a novel Ca(2+) pump. [Extracted from the article]

The article presents a case study of a 57-year-old woman with no medical history visiting her dermatologist for a chronic itching dermatosis as well as a similar skin disorder that was found in the 53-year-old sister of the patient. The sisters were identified a new heterozygous nonsense mutation, p.Arg272 in POGLUT1 gene encoding the O-glucosyltransferase 1 enzyme. The authors discuss Dowling-Degos (DD) disease as a rare autosomal-dominant genetic disorder in reticulated pigmented dermatitis.