[A Case of Recurrent Breast Cancer with Drug-Induced Interstitial Pneumonia Triggered by the Switch from an Original to a Generic Aromatase Inhibitor].

We report the case of a 72-year-old woman who had undergone mastectomy for left breast cancer 9 years ago and had received anastrozole for 6 years after the operation. A year ago, she experienced a breast cancer recurrence in the thoracic wall and lymph nodes and was re-administered anastrozole, leading to a shrinking of the recurrent tumor. After the change from anastrozole to a generic product 2 months ago, she experienced respiratory distress. A CT scan showed bilateral reticular and ground-glass shadows in the lung fields, leading to the diagnosis of interstitial pneumonia, which was treated with steroids. When the generic product was restarted after the symptom had resolved, a recurrence of the lung lesions was observed. Therefore, VATS was performed and a histopathological diagnosis of interstitial pneumonia was posed. We then switched to letrozole, but because of the reappearance of the same lung lesions, the drug was discontinued, and the course was observed. Six months after, the re-expansion of breast cancer metastases was observed. When exemestane was initiated, the lung lesions recurred. The patient's condition improved on a steroid pulse and artificial respiration; however, she died of aspiration pneumonia. We report a case of recurrent breast cancer with drug-induced interstitial pneumonia triggered by the switch from an original to a generic aromatase inhibitor.