Cutaneous sarcomatoid B-cell lymphoma.

A rare case of a spindle cell (sarcomatoid) B-cell lymphoma is described. The patient, a 48-year-old male, presented with a several month history of an enlarging lesion on the scalp. Although there have been a few recent reports of cutaneous sarcomatoid lymphomas, this case is especially unusual because it presented as a scarlike plaque rather than a tumor and microscopically exhibited a prominent myxoid matrix. Given these features, the lesion was initially interpreted as an atypical fibromucinosis. The differential diagnosis included fibromucinous lesion consistent with variant of lichen myxedematosus, spindle cell carcinoma, spindle cell melanoma, atypical fibroxanthoma, and atypical smooth muscle tumors. Initial immunoperoxidase studies demonstrated negative staining for CD68, factor XIIIa, CD57, cytokeratin(AE1/AE3), S100, EMA, and vimentin, essentially ruling out the previously mentioned neoplasms. Subsequently, strong positive staining for LCA(CD45RB) and CD20 was demonstrated characteristic of a B-cell lymphoma. The patient underwent local radiotherapy with complete resolution. Although all variants of cutaneous sarcomatoid B-cell lymphomas are rare, it is imperative to consider them in the differential diagnosis of otherwise difficult to categorize spindle cell proliferations. This includes neoplasms and, based on the current case, fibromucinoses as well.