Breast Cancer in Patients of Rheumatoid Arthritis with Methotrexate Therapy Mimicking Histopathological Changes after Neoadjuvant Chemotherapy.

Two breast cancer patients with a history of treatment for long-term rheumatoid arthritis (RA) had histological findings similar to histological changes seen in resected mammary gland specimens following neoadjuvant chemotherapy (NAC). The first patient was a 64-year-old woman who visited our hospital after feeling a lump in her left breast. The second patient was a 68-year-old woman who visited our hospital for an indentation in her left nipple. They were diagnosed with breast cancer following detailed examinations and underwent mastectomy. Both patients had a history of RA and were being treated with Methotrexate. The histological diagnoses of these patients were invasive ductal carcinoma, but frequent dispersal of cancer cell nests, stromal fibrosis, elastosis, edema and inflammatory cell infiltration were seen. Fibrosis was also found in the dissected lymph node. These histological findings were extremely similar to changes that occur in the mammary gland tissue after NAC; however, these patients had not undergone NAC. Methotrexate, which was being administered as an anti-rheumatic drug to the two patients, might have played a role similar to that of metronomic chemotherapy, which involves the continuous use of low-dose anti-cancer drugs, resulting in histological changes similar to those seen after NAC.