First Reported Case of Pure Red Cell Aplasia Related to Sotorasib.

We herein report a 64-year-old man with KRASG12C-mutated advanced lung adenocarcinoma previously treated with immune checkpoint inhibitors (ICIs). One month after starting second-line sotorasib treatment, the patient experienced a progressive decline in serum hemoglobin levels. Anemia was accompanied by markedly elevated serum erythropoietin levels and decreased reticulocyte levels. Bone marrow aspiration revealed pure red cell aplasia. No secondary causes other than medication use were identified. Suspected causative drugs were sotorasib and ICIs. Discontinuation of sotorasib for one week improved his anemia; therefore, the causative drug was identified as sotorasib.