Malignant Trichoepithelioma Mimicking Basal Cell Carcinoma: A Rare Follicular Adnexal Malignancy

Malignant trichoepithelioma is a rare follicular adnexal malignancy with overlapping features of trichoblastic carcinoma. It is characterized by follicular germinative differentiation with mixed basaloid and squamoid morphology.[1,2] The lesion may closely mimic basal cell carcinoma or squamous cell carcinoma on routine microscopy. We report a rare scalp lesion in a 58-year-old male presenting as a progressively enlarging ulceroproliferative growth. Histopathological examination revealed infiltrative nests, cords and lobules of atypical epithelial cells showing basaloid morphology with focal squamoid differentiation, keratin pearl formation, horn cyst-like structures, stromal desmoplasia, brisk mitotic activity and focal necrosis.[5,6] Immunohistochemistry showed positivity for BerEP4, CK5/6, Bcl-2 and PHLDA1 with elevated Ki-67 labeling index, supporting follicular adnexal differentiation and malignant transformation.[7,8] This case illustrates the diagnostic difficulty encountered in differentiating follicular adnexal tumors from other keratinizing cutaneous neoplasms. Our findings emphasize the importance of clinicopathological correlation in rare adnexal tumors.