Primary Cutaneous Diffuse Large B-Cell Lymphoma, Leg Type, With Spontaneous Regression After Biopsy.

Primary cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL-LT) represents approximately 20% of cutaneous B lymphomas with an intermediate prognosis. Spontaneous regression is uncommon; there are only 2 published cases. An 83-year-old woman presented 2 orange erythematous nodules on the back of her right leg with an elastic consistency, infiltrated, painful to the touch, and of an 8-month evolution. A histological examination revealed a dense cellular dermo-hypodermic infiltrate sparing the papillary dermis, composed of large cells with immunoblast and centroblast morphology and frequent mitosis. Immunohistochemical studies showed positivity for CD20, CD79, Bcl2, Bcl6, MUM1, Fox-P1, and IgM with Ki67 >95%. Rearrangement of heavy IgH chains was monoclonal. The extension study was negative, establishing a diagnosis of PCDLBCL-LT, T2aN0M0. Three months after biopsy, the patient's lesions regressed spontaneously. New biopsies were taken that revealed a mild diffused dermo-hypodermic cellular infiltrate compounded by small-sized T lymphocytes, with predominance of CD8. Despite its self-limited character, treatment with radiotherapy was done, remaining asymptomatic after 1 year follow-up. There are 2 published cases of PCDLBCL-LT with spontaneous regression. The cause of this unusual autoinvolutional phenomenon is unknown; it may be an immune response against tumor cells through a traumatic or infectious mechanism.