Primary cutaneous carcinosarcomas: a morphological histogenetic concept revisited.

To present and define diagnostic criteria for primary cutaneous carcinosarcomas (CSs). Neoplasms of 6 patients with primary cutaneous CSs were retrospectively analyzed. A panel of histopathologic parameters and immunophenotypic expression of distinct markers of differentiation were investigated. All cases had medium-to-poorly differentiated squamous cell carcinoma representing the epithelial component intermingled with a variable amount of malignant sarcomatous tissue proliferation. The authors identified 3 distinct morphological criteria for the diagnosis of primary cutaneous CSs with features of (1) a clearly defined dual neoplasm with explicit morphological characterization using histology and immunohistochemistry with distinct marker panels while, (2) metastases from distant sites and true collision neoplasms must be excluded, and (3) recognition of the neoplasm as a solid coherent proliferation with careful exclusion of sarcomatous stromal changes in the surrounding neoplasm stroma has to be assured. The low incidence of this entity and a plethora of different synonymous terms in the dermatopathologic literature often cause diagnostic problems and hamper the accurate comparative analysis of cases published previously. Herein, the authors propose defining criteria and a clearly defined morphological approach to contribute to more accurate dermatopathologic diagnoses and provide an unprecedented summary on this neoplastic entity.