The expression of IgM is helpful in the differentiation of primary cutaneous diffuse large B cell lymphoma and follicle center lymphoma.

Diffuse large B-cell infiltration of the skin includes mainly primary cutaneous follicle center lymphoma (PCFCL) with diffuse architecture and diffuse large B cell lymphoma (PCDLBCL), leg type. Differentiation of these lymphomas on morphology may be troublesome. Immunohistochemistry panel, including CD20, CD79a, bcl-6, bcl-2, MUM-1, FOX-P1 is mandatory. However, in minority of cases, these markers would not suffice. In order to search the value of another marker, IgM, 30 cases of PCFCL and 10 cases of PCDLBCL, leg type were included in the study. As suggested in a recent literature, our study denoted that expression of IgM was useful as an additional tool for differentiation.