Unexpected Fatal Pneumocystis Jirovecii Pneumonia During Triplet Therapy for Hormone-Sensitive Prostate Cancer.

Pneumocystis jirovecii pneumonia (PJP) is a life-threatening opportunistic infection typically seen in immunocompromised patients. It is rarely reported during standard systemic therapy for prostate cancer. A 75-year-old man with low-volume metastatic hormone-sensitive prostate cancer (mHSPC) received triplet therapy with relugolix, darolutamide and docetaxel. He had well-controlled diabetes and no history of immunosuppression. After the second docetaxel cycle, he developed anorexia. Chest CT revealed bilateral ground-glass opacities. β-D-glucan was elevated, and sputum PCR detected P. jirovecii DNA. Despite appropriate trimethoprim-sulfamethoxazole and corticosteroid therapy, he died of respiratory failure ~10 days after symptom onset. This case highlights an underrecognized risk of PJP during triplet therapy for mHSPC. Prophylaxis should be considered in select high-risk patients, including elderly individuals or those with metabolic comorbidities.