Recurrent Secondary Organizing Pneumonia During Adjuvant Letrozole Therapy Following Breast Cancer Radiotherapy: A Case Report

Aromatase inhibitors are a cornerstone of adjuvant endocrine therapy for hormone receptor-positive breast cancer and are generally associated with a favorable safety profile.However, rare pulmonary toxicities, including organizing pneumonia, have been sporadically reported.Secondary organizing pneumonia (SOP) is an uncommon inflammatory pulmonary disorder that may occur in association with infections, autoimmune diseases, radiation exposure, or drug-induced toxicity.We report the case of a 69-year-old woman who developed recurrent SOP during adjuvant letrozole therapy following surgery, chemotherapy, and locoregional radiotherapy for hormone receptor-positive early-stage breast cancer.The patient presented with bilateral pulmonary infiltrates characterized by ground-glass opacities and consolidative changes, predominantly involving previously irradiated lung regions.Extensive diagnostic evaluation excluded infectious, malignant, and other potential etiologies.Initial treatment with systemic corticosteroids resulted in rapid clinical and radiological improvement.However, multiple relapses occurred during corticosteroid tapering while letrozole therapy was continued.Following multidisciplinary evaluation and discontinuation of letrozole, complete radiological resolution was achieved, and no further recurrences were observed during follow-up.The temporal relationship between letrozole exposure, recurrent inflammatory pulmonary manifestations, repeated corticosteroid responsiveness, and sustained recovery after drug withdrawal suggests a possible association between letrozole therapy and SOP.Prior thoracic irradiation may have contributed to increased susceptibility to pulmonary injury.Although the underlying mechanisms remain poorly understood, immune-mediated pathways and persistent inflammatory activation within previously irradiated lung tissue may play a role.This case highlights the importance of considering aromatase inhibitor-associated organizing pneumonia in breast cancer survivors presenting with recurrent pulmonary infiltrates, particularly when symptoms recur despite corticosteroid therapy and alternative causes have been excluded.