Morpheaform basal cell carcinoma clinically manifests as a white, scarlike patch or plaque with ill-defined borders. Histologically, the tumor forms cords and strands of basaloid cells that infiltrate a dense collagen stroma. Although the histologic appearance is similar to a microcystic adnexal carcinoma, basal cell carcinomas usually do not have ductal structures or horn cysts, and they may exhibit features of typical basal cell carcinomas, such as stromal retraction and mucin deposition.
Syringomas are benign eccrine neoplasms that exhibit small ducts embedded in a sclerotic stroma. The ducts may have elongated tails of epithelial cells, forming tadpole-like structures. Deep infiltration of epithelial cells is not seen.
Pseudoglandular squamous cell carcinoma demonstrates a proliferation of atypical keratinocytes that form invasive, glandular structures. Ductal structures are not seen.
Metastatic adenocarcinoma demonstrates atypical, pleomorphic cells forming glandular structures in the dermis. Mucin deposition may be present. These lesions do not demonstrate horn cysts or ductal structures.
Microcystic adnexal carcinomas are poorly circumscribed eccrine tumors that demonstrate infiltrative epithelial cords associated with a sclerotic stroma. Horn cysts, ducts, and glandlike structures may be seen. Tumors cells may extend into the subcutis and skeletal muscle, and perineural invasion is common.
