Erythrocytosis as an indicator of disease progression of small cell lung cancer: A case report.

This case involves a 62-year-old male diagnosed with extensive-stage small cell lung cancer (ES-SCLC) originating from the right lower lobe with brain metastases. The patient underwent stereotactic radiosurgery (SRS) and received four cycles of combination therapy with cisplatin, etoposide, and durvalumab, followed by maintenance therapy with durvalumab to achieve disease control. On day 156 after treatment initiation, hemoglobin (Hb) levels increased to 16.9 g/dL, indicating polycythemia. Concurrently, new brain metastatic lesions were identified, and serum erythropoietin (EPO) levels were markedly elevated at 406 mIU/mL. Whole-brain radiation therapy (WBRT) was initiated, resulting in a subsequent reduction in hemoglobin levels and improvement in polycythemia. This report describes a rare case of secondary polycythemia associated with ES-SCLC. Notably, WBRT appeared to contribute to the normalization of serum EPO levels and resolution of polycythemia. This report elucidates the clinical course and relevance of this condition based on a literature review.