Basal cell carcinoma with matrical differentiation.

Three cases of basal cell carcinoma showing shadow cells within basaloid islands have been described using the term basal cell carcinoma with matrical differentiation for this histologic variant. We present four new cases of basal cell carcinoma with evidence of matrical differentiation. Unlike the cases previously published, these lesions showed nests of shadow cells either within the lobules of basaloid cells or forming nests in the stroma. We also noted the presence of a foreign body reaction and calcification. These neoplasms illustrate the capability of basal cell carcinoma to differentiate toward hair matrix cells. Basal cell carcinoma with matrical differentiation must be added to the uncommon variants of basal cell carcinoma showing adnexal differentiation. A parallel between the degrees of differentiation of the cutaneous sebaceous neoplasms with those showing matrical differentiation is proposed.