Supplementary Material for: Pure red cell aplasia induced by atezolizumab in a patient with small cell lung cancer successfully treated with steroid therapy: a case report

Introduction: Combination therapy of atezolizumab and chemotherapy has become the standard treatment for small-cell lung cancer. Immune-related adverse events (irAEs) can occur during immune checkpoint inhibitor administration. A few reports exist on pure red cell aplasia (PRCA) as an irAE after atezolizumab treatment. PRCA is characterized by normocytic-normochromic anemia, a marked decrease in reticulocytes, and a decrease in bone marrow erythroblasts. Here, we report a case of atezolizumab-induced PRCA.

Case presentation: A 69-year-old male patient was brought to the emergency department with the chief complaint of seizures. Multiple metastatic brain tumors and a mass suspected to be the primary lesion in the right hilar region were observed. After a brain biopsy, he was diagnosed with small-cell lung cancer (cT1cN0M1c cStage IVB). He received four courses of carboplatin, etoposide, and atezolizumab in combination with whole-brain irradiation, which led to a partial response. After six courses of atezolizumab maintenance therapy, severe anemia (hemoglobin, 3.4 g/dL) was observed. PRCA induced by atezolizumab was diagnosed using a bone marrow biopsy performed during a red blood cell transfusion. Treatment was started with prednisolone 25 mg/day (0.5 mg/kg/day). The anemia improved, and the dose was gradually reduced to 5 mg/day.

Conclusion: Reports of PRCA as an irAE are rare but important; hence, we reported this case.