Case Report: A rare case of Pneumocystis jirovecii infection with left hydropneumothorax following immunotherapy for stage IVB clear cell renal cell carcinoma.

Background: Pneumocystis jirovecii pneumonia (PJP) is an opportunistic infection that predominantly affects immunocompromised individuals, most commonly HIV-infected patients with significantly reduced CD4+lymphocyte counts, and is associated with high clinical mortality. Currently, there are few reports of pneumothorax secondary to PJP, and most cases occur in HIV-infected populations. However, PJP complicated by hydropneumothorax in cancer patients receiving immunotherapy is exceedingly rare, with limited reports in the literature. To our knowledge, this article reports a rare clinical case of Pneumocystis jirovecii infection complicated by left-sided hydropneumothorax in a patient with stage IVB clear cell renal cell carcinoma after immunotherapy, aiming to provide valuable insights for the early diagnosis and management of PJP and its complications in cancer patients undergoing immunotherapy. Case: A 57-year-old male patient had previously undergone surgical treatment for left renal clear cell carcinoma, and developed recurrent metastases to the descending colon, liver, and upper pole of the left kidney after surgery, with a clinical stage of T4NxM1 stage IVB. After receiving targeted combination immunotherapy with sequential PD-1 inhibitors (toripalimab) plus anti-angiogenic agents (sunitinib, axitinib)-a regimen that enhances anti-tumor immunity but may disrupt pulmonary immune homeostasis-the patient gradually developed progressive dyspnea, chest tightness, hypoxemia, and anuria. Multiple auxiliary examinations were performed clinically, including chest X-ray, bronchoalveolar lavage, and metagenomic sequencing of pathogenic microorganisms. Based on the above examination results, the final diagnosis was Pneumocystis jirovecii pneumonia complicated by left-sided hydropneumothorax. Conclusion: Although PJP complicated by hydropneumothorax after immunotherapy is rare, it should be considered as a possible etiology when cancer patients develop progressive dyspnea with difficulty maintaining oxygen saturation after receiving immune checkpoint inhibitor-based therapy, particularly in the context of immune checkpoint inhibitor use. While biomarkers for predicting immunotherapy efficacy and irAEs are well-studied, the identification of specific biomarkers for predicting opportunistic infections like PJP in this context remains an area of active research.