Carcinosarcoma. (a) The epithelial component with features of basal cell carcinoma admixed with the mesenchymal fibrosarcomatous component. (b) Close-up of the pleomorphic sarcomatous and carcinomatous components
Carcinosarcoma. (a) An epithelial component represented by a malignant basaloid adnexal tumor with features of porocarcinoma. (b) The malignant mesenchymal component admixed with the epithelial proliferation made by reticulated and irregularly anastomosing cords with ductal spaces. (c) The malignant mesenchymal component is made by spindle cells with pleomorphic nuclei and features of undifferentiated sarcoma. (d) P-63 positivity in the porocarcinomatous component. (e) Positive staining for CEA in the luminal ducts. (f) Ki-67 showing high proliferative index in the sarcomatous component
A combination of wide spectrum cytokeratin, glandular epithelial markers, and p63 (Figs. 6.2d, e) is helpful in the distinction of CS from other spindle cell neoplasms, while immunohistochemistry for smooth muscle actin, desmin, and myogenin may be useful in confirming smooth or skeletal muscle differentiation.
CD10 and podoplanin (D2-40) have diagnostic utility in differential with atypical fibroxanthoma that shows a strong and diffuse positive pattern of staining, while CS is negative. High proliferative index with Ki67 is easy to find in both components (Fig. 6.2f).
Identical mutations of both the tumor suppressor gene p53 and patched gene (PTCH1) have been reported in both the epithelial and the mesenchymal components, suggesting a clonal origin of the tumor.
The diagnosis is only a histological one and may be challenging; CS should be distinguished from other microscopic spindle cell tumors such as atypical fibroxanthoma, spindle cell squamous cell carcinoma, and spindle cell malignant melanoma.
Cutaneous metastases of soft tissue or bone sarcomas may enter the differential diagnosis but are extremely rare, and only anecdotal cases have been reported.