Squamous cell carcinoma of the skin: dual differentiations to rare basosquamous and spindle cell variants

Basosquamous carcinoma (BSC) is defined as a tumor containing the areas of both basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) with a transition zone linking the two. Spindle cell squamous carcinoma (SCSC) may have a variable component of conventional SCC and spindle cells. We present a case of an 89-year-old woman with an eruption on the scalp for several decades. Grossly, the lesion measured 8.5 x 6.0 x 1.8 cm and consisted of a gray-white and focally black tumor. Microscopically, a non-ulcerated upper part of the tumor consisted of large polygonal squamoid cells with occasional keratinization (SCC), trabecular growth of basaloid cells with peripheral palisading (BCC), and an area in which both the components were intermingled. The rest of the tumor was a myxoid area with elongated fusiform spindle cells, which appeared to arise from conventional SCC. Immunohistochemically, the tumor cells in the SCSC (both conventional and spindle cell) area co-expressed CAM5.2, and vimentin. Ber-EP4 was positive in the BCC area with the transition zone of SCC and BCC showing diminished staining. Epithelial membrane antigen was focally positive in the conventional SCC area. To our knowledge, this is the first case report of SCC of the skin that has dual differentiations to BSC and SCSC.