Letrozole-Induced Pneumonitis Complicated by Acute Respiratory Distress Syndrome: A Case Report

Letrozole is a commonly used aromatase inhibitor in the adjuvant treatment of hormone receptor-positive breast cancer and is generally well tolerated. Pulmonary toxicity is rare and poorly described. We report the case of a 74-year-old woman who developed progressive respiratory symptoms over two months, initially suggestive of infectious pneumonia, but with negative microbiological investigations and no response to multiple antibiotic therapies. Her condition worsened, leading to acute respiratory distress syndrome requiring invasive mechanical ventilation. A drug-induced pneumonitis related to letrozole was suspected. Discontinuation of the drug and initiation of corticosteroid therapy resulted in rapid clinical improvement. This case highlights a rare but potentially severe pulmonary adverse effect that should be considered in patients with unexplained pneumonia.