Case 1 involved a 75-year-old woman with breast cancer and diffuse large B-cell lymphoma(DLBCL).Although we initially administered the R-CHOP regimen, the breast tumor increased in size and surgery had to be performed.After surgery, the R-CHOP regimen was re-initiated and DLBCL achieved clinical complete response.Case 2 involved a 74-year-old woman with breast cancer and gastric MALT lymphoma.After administration of rituximab and H. pylori eradication, a therapeutic effect was achieved in the lymphoma.A docetaxel and FEC regimen was continuously administered and surgery was performed. Case 3 involved a 62-year-old woman with breast cancer and follicular lymphoma.She presented with a history of DLBCL treatment.We performed mastectomy and sentinel lymph node biopsy, which revealed metastasis of breast cancer, and axillary lymph node dissection was subsequently performed.Considering the pathological stage, adjuvant chemotherapy was needed.We selected the TCH regimen based on her past treatment.In conclusion, it is necessary to treat patients with double presentation of breast cancer and malignant lymphoma through cooperation with different departments.