Cutaneous follicular lymphoma.

Fifteen cases of cutaneous follicular lymphoma were evaluated clinically, histologically, and immunologically. Nine of the patients presented with skin disease alone, which showed a predilection for the scalp and forehead. The six remaining cases had either concurrent or secondary cutaneous involvement. All of the cases had a nodular configuration which was evident histologically or immunologically. In many cases, the diagnostic microscopic fields were in the deep dermis or subcutis, with nonspecific inflammation in the superficial dermis. The cases consisted of five small cleaved, seven mixed, and three large cell follicular lymphomas. A senior dermatopathologist diagnosed four of the 15 cases as benign, indicating the difficulty of diagnosis by morphology alone when the biopsy is small or the inflammatory component is prominent. This underscores the importance of large, deep biopsies for accurate histologic diagnosis. Immunological studies confirmed the B cell lineage of these lesions. An unexpectedly high proportion of immunoglobulin-negative cases (eight cases) was found, especially among the primary cutaneous follicular lymphomas (six of nine cases). Immunoglobulin-expressing cases exhibited monotypic immunoglobulin light-chain staining of tumor cells. In all cases, the dendritic reticulum cell network within lymphoma follicles lacked the polytypic immunoglobulin complexes characteristic of reactive follicles. As described previously for follicular lymphomas in lymph nodes, many cases exhibited polytypic follicular mantle zones similar to reactive follicles. The low-grade nature of these lymphomas was supported by clinical follow-up. We conclude that given adequate sampling, cutaneous follicular lymphomas can usually be diagnosed by histologic criteria similar to those used for lymph nodes; however, immunohistologic studies are an important adjunct.