Fatal Interstitial Pneumonitis During Combined Degarelix, Darolutamide, and Docetaxel Therapy for Metastatic Prostate Cancer.

Triplet therapy for metastatic hormone-sensitive prostate cancer improves survival but may rarely cause severe pulmonary toxicity. A 79-year-old man with low-volume metastatic prostate adenocarcinoma (PSA 613 ng/mL) received degarelix, darolutamide, and docetaxel. After the fifth docetaxel cycle, he developed a low-grade fever and exertional dyspnea. Chest computed tomography revealed diffuse, non-segmental bilateral ground-glass opacities. Microbiologic evaluation, including β-D-glucan and Pneumocystis jirovecii PCR, was negative, and clinically suspected drug-induced interstitial pneumonitis was diagnosed. Anticancer therapy was immediately discontinued, and two courses of high-dose intravenous methylprednisolone pulse therapy were administered, followed by oral corticosteroid tapering. Despite early intervention, radiologic abnormalities progressed, and hypoxemia worsened, ultimately resulting in fatal respiratory failure. Notably, serum PSA declined to 0.07 ng/mL and remained suppressed throughout the period of pulmonary deterioration, indicating a sustained oncologic response despite lethal toxicity. This case underscores that life-threatening interstitial lung disease may occur during docetaxel-based triplet therapy even in the absence of preexisting pulmonary risk factors. Early imaging for subtle respiratory symptoms and prompt multidisciplinary management are essential to mitigate potentially fatal outcomes.