Abstract: Primary cutaneous diffuse large B-cell lymphoma-leg type (PCDLBCL-LT) is a rare form of skin B-cell lymphoma with a high risk of aggression and recurrence. We report a 47-year-old male with erythema annularis on the right lumbar for 1 month. Pathology showed a large number of heterogeneous lymphocyte infiltrates in the lesion, immunohistochemical CD20, CD79a, Bcl-2 positive, Ki-67 proliferation index up to 80%. After five courses of chemotherapy with R-CHOP regimen, the skin lesions completely subsided, and no recurrence was observed during the follow-up of two and a half years. This case suggests that PCDLBCL-LT may be manifested as annular granulomatous lesions, which is easy to misdiagnose. It is necessary to confirm the diagnosis by combining pathology and immunohistochemistry, and timely systematic treatment to improve the prognosis.

Key words: primary cutaneous diffuse large B-cell lymphoma, leg type, annular, rituximab