Basal Cell Carcinosarcoma with an Osteosarcomatous Component: A Case Report Supporting the Diagnostic Utility of SATB2 and TRAP Immunostaining with a Literature Review of 22 Cases

ABSTRACT: Basal cell carcinoma rarely coexists with malignant mesenchymal component(s), termed as basal cell carcinosarcoma (BCCS). BCCS often comprises an osteosarcomatous change, which considerably varies in the histological extent among reported cases. Owing to its rarity and morphological heterogeneity, the disease may be underrecognized and pose accurate diagnosis and treatment approaches. In this study, we present a case of BCCS with a focal osteosarcomatous component in a 91-year-old woman with a rapidly enlarging solitary tumor on the left cheek. Histopathological examination revealed a biphasic tumor composed of conventional basal cell carcinoma and a high-grade sarcomatous component, both of which were intermingled gradually in the transitional zone. Limited portions of the sarcomatous component contained atypical spindle-to oval-shaped cells and osteoclast-like multinucleated giant cells surrounded by an osteoid matrix. Immunohistochemically, these cells were positive for an osteoblastic marker SATB2 and an osteoclast-associated marker tartrate-resistant acid phosphatase, respectively, but negative for epithelial markers AE1/AE3 and BerEP4. These findings supported a diagnosis of BCCS with an osteosarcomatous component. To the best of our knowledge, literature review identified only 21 similar cases thus far reported, but no previous reports have used a combined use of SATB2 and tartrate-resistant acid phosphatase immunostaining to substantiate the osteosarcomatous focus in cutaneous carcinosarcoma. Our case may highlight the potential diagnostic value of these 2 markers in distinguishing the true osteosarcomatous components from mimicking elements such as dystrophic calcification or hyalinized collagen deposition, but also in detecting a subtle osteosarcomatous component in carcinosarcoma.