Which tumor is the true basal cell carcinoma?

Skin Tumors

Which one is the true Basal Cell Carcinoma?

Diagnosis:

Case 1: Basaloid Follicular Induction overlying a dermatofibroma

Case 2: Nodular Basal Cell Carcinoma overlying a dermatofibroma

Both cases show classical histological features of dermatofibroma in dermis.  In case 1, basaloid  proliferation is seen at the undersurface of the epidermia, which is easily misdiagnosed as superficial basal cell carcinoma. While in case 2, a truly de novo basal cell carcinoma is seen. Tissue necrosis is present which is highly suggestive of malignancy.

Epidermal changes such as hyperplasia and hyperpigmentation are common in dermatofibroma. In 5-8% of cases there is a spectrum of basaloid proliferation at the dermoepidermal junction ranging from basaloid hyperplasia to basal cell carcinoma. The basaloid hyperplasia may represent hair follicular remnants that are regressed and forced upward by the dermal spindle cell proliferation. Alternatively, they have been interpreted as being the result of hair follicle induction by the fibrous proliferation. Basal cell carcinoma has been reported to arise over dermatofibromas, but many of the proliferations probably are just histologic mimics of basal cell carcinoma, indicated by the presence of papillary mesenchymal bodies. The unequivocal distinction is not easy. Cleft formation, mitosis and necrosis are signs of an expansile growth, which are features of basal cell carcinoma.

Submitted by Yong Tao, M.D., PhD.

Reference:

Goette DK, Helwig EB. Basal cell carcinomas and basal cell carcinoma-like changes overlying dermatofibromas. Arch Dermatol. 1975 May;111(5):589-92.

Comments:

Thank you for sharing this case. It is very well illustrated.  Even after all of the discussion the distinction is difficult.