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Cutaneous metastasis as a primary presentation of a pulmonary enteric adenocarcinoma

Background: Primary pulmonary enteric adenocarcinoma (PEAC) is a rare non-small cell lung cancer subtype sharing morphologic and immunohistochemical features with colorectal adenocarcinoma. Given the frequency of lung metastases in colorectal cancer, the differential diagnosis of PEAC according to routine morphological and immunohistochemical findings may be difficult. Genome sequence by next-generation sequencing has recently introduced new perspectives to better define the diagnosis and tumor sensitivity to treatments, while the rarity of this subtype of cancer still limits the current knowledge of its molecular features and provides no information to address patients to tailored therapies. Methods: We diagnosed a rare case of subcutaneous metastasis as a first symptom of a PEAC. Formalin-fixed paraffin-embedded samples of the primary tumor and subcutaneous metastases were examined by immunohistochemistry, and subsequently by targeted next-generation sequencing analysis. Results: Morphological and immunohistochemical findings suggested a rare case of metastatic pulmonary adenocarcinoma with enteric aspects. Next-generation sequencing analysis performed on both the primary tumor sample and the cutaneous lesion identified two pathogenic variants on CDKN2A and KRAS in both of them. However, the metastasis showed two additional pathogenic mutations located in SMAD4 and FLT3 genes. Conclusions: We describe for the first time an extensive molecular analysis on a rare case of PEAC with an unusual cutaneous metastasis. Our observation suggests that a specific pattern of mutations is harbored in this neoplasm, and that additional molecular studies may provide further information to identify prognostic and hopefully predictive genes of response to treatment.