A case of bilateral methotrexate-associated diffuse large B-cell lymphomas of the breasts with unique clinical presentation and outcome.

: A 54-year-old woman on methotrexate (MTX) treatment developed reddish skin change in her right breast. Mammography and ultrasound showed no masses in the breasts but bilateral mammary glands presented diffuse lower-level echoes. Only 19 days later, the patient developed bilateral breast masses. Histological examination showed that diffuse large B-cell lymphoma cells spread widely and sparsely in the bilateral breasts in addition to the tumor cell conglomerate, leading to the diagnosis of MTX-associated lympho-proliferative disorders (MTX-LPDs). Withdrawal of MTX resulted in complete disappearance of the left MTX-LPD in 2 months but no regression of the right MTX-LPD. Chemotherapy led to a partial response followed by re-growth of the right MTX-LPD. Re-biopsy of the right MTX-LPD revealed double/triple hit lymphoma. Second-line and later-line chemotherapies caused no regression of the right MTX-LPD. The patient died in a year after the diagnosis of MTX-LPDs. Breast oncologists should note the presence, biology, and diagnostic images of MTX-LPD.