Organizing Pneumonia Associated with <i>Pneumocystis jirovecii</i> in a Patient Receiving Dose-Dense Chemotherapy for Breast Cancer: A Case Report

In patients not infected by HIV, Pneumocystis jirovecii pneumonia (PCP) is characterized by rapid disease progression, difficulty in confirming the diagnosis, and poor prognosis. PCP has also been reported in immunocompromised patients receiving chemotherapy, most often for hematologic tumors, although some patients receiving treatment for breast cancer have been affected. Dose-dense chemotherapy (DDC) which is performed with shorter dosing intervals than standard chemotherapy and is now widely used in clinical practice. However, adverse events have been reported, including infections associated with decreased immune status. PCP infection is considerably more challenging to diagnose and treat than bacterial or viral infections. Furthermore, organizing pneumonia (OP), a pulmonary lesion of PCP, is infrequent and requires caution on the part of clinicians, as protozoan infections require different forms of treatment. Although we initially suspected bacterial, viral, and drug-induced pneumonia in our patient and started treatment with antibiotics, antifungals, and prednisolone, the final diagnosis was OP. The pulmonary lesion of PCP was treated with systemic corticosteroids, leading to recovery. There have been no similar reports of PCP during chemotherapy for malignant disease; however, the possibility of OP should be considered during chemotherapy. Herein, we report a case of PCP during preoperative DDC for advanced breast cancer.