Pneumocystis jirovecii Pneumonia in an HIV-Negative Patient Receiving Adjuvant Capecitabine and Oxaliplatin (CAPOX) Chemotherapy for Colon Adenocarcinoma: A Case Report.

Pneumocystis jirovecii pneumonia (PJP) is a potentially life-threatening opportunistic infection, classically associated with human immunodeficiency virus (HIV) infection but increasingly recognized in non-HIV immunocompromised hosts, including patients with solid tumors undergoing chemotherapy. We present the case of a 57-year-old woman with stage II (pT3N0M0) mucinous colon adenocarcinoma who developed PJP following adjuvant capecitabine and oxaliplatin (CAPOX) chemotherapy, without exposure to prolonged corticosteroids or severe cytopenia. The patient presented with progressive exertional dyspnea and a productive hemoptoic cough the week after the last chemotherapy cycle. Laboratory tests revealed mild lymphopenia with preserved neutrophil counts and elevated lactate dehydrogenase (LDH). Chest computed tomography demonstrated bilateral ground-glass opacities, and bronchoalveolar lavage (BAL) confirmed the presence of P. jirovecii by immunofluorescence. Treatment was initiated with intravenous trimethoprim-sulfamethoxazole for seven days, followed by two weeks of oral therapy, without adjunctive corticosteroid therapy. The patient made a full clinical recovery. This case highlights the need to consider PJP in non-HIV immunosuppressed patients, particularly those with solid tumors receiving chemotherapy, even in the absence of classical risk factors such as severe cytopenia or prolonged corticosteroid use. Early diagnostic suspicion and targeted microbiological testing are essential, given the rapid progression and high mortality associated with PJP in this population.