Intestinal adenosquamous carcinoma with a synchronous skin metastasis: a immunohistochemical and molecular analysis

Introduction: Intestinal adenosquamous carcinoma (ASC) is a rare colorectal neoplasm frequently occurring at onset as a locally advanced disease with distant metastases. The liver is the most common site of metastasis, followed by the peritoneum and the lung. Cutaneous metastases from usual colorectal adenocarcinoma occur in about 3% of cases, both at the time of diagnosis in advanced disease and during the follow-up. To the best of our knowledge, skin metastasis from ASC has never been described, and no biological landscape of ASC has ever been investigated. Methods: We report a case of synchronous intestinal ASC and cutaneous single facial metastasis in a 70-year-old man with morphological, immunohistochemical, and molecular analysis of primary and metastatic lesions. Results: Primary and metastatic ASC showed the same morphological and immunohistochemical features. Target sequencing analysis revealed, both in primary tumor and metastasis, a pathogenic KRAS gene missense mutation c.38G > A p.(Gly13Asp) and a likely pathogenic CTNNB1 gene missense mutation c.94G > A p.(Asp32Asn). A nuclear localization of β-catenin protein in adenocarcinomatous component of primary and metastatic lesions was observed on immunohistochemistry. Conclusion: We describe a case of single synchronous facial cutaneous metastasis from intestinal ASC showing KRAS and CTNN1B mutations both on primary and metastatic lesions.