Capecitabine-induced pneumonitis: a rare case report and literature review.

Capecitabine is an oral fluoropyrimidine prodrug widely used in the treatment of various malignancies, including colorectal cancer. While it is generally well-tolerated, rare and life-threatening toxicities can occur. Pneumonitis is an exceedingly rare complication associated with capecitabine monotherapy. A 36-year-old male with pT3N0 (stage IIA) colon adenocarcinoma underwent curative resection and was started on adjuvant capecitabine monotherapy. During the second cycle, the patient developed a cough and exertional dyspnea. Symptoms progressed during the third cycle, leading to hospitalization. Imaging revealed diffuse ground-glass opacities, and pulmonary function tests showed a severely reduced diffusion capacity of the lung for carbon monoxide (38% of predicted). Dihydropyrimidine dehydrogenase deficiency was ruled out. Based on clinical and radiological findings, a diagnosis of capecitabine-induced pneumonitis was made. Capecitabine was discontinued, and intravenous methylprednisolone (1 mg/kg) was initiated. The patient showed rapid symptomatic improvement and was discharged with a tapered steroid regimen. Follow-up imaging at 1 month showed complete resolution of pulmonary opacities. The patient remains in remission at a 3-year follow-up. Although capecitabine-induced pneumonitis is remarkably rare, it carries a risk of significant morbidity. Clinicians should maintain a high index of suspicion for drug-induced pulmonary toxicity in patients presenting with new respiratory symptoms during capecitabine therapy, as early recognition and treatment are crucial for recovery.