A Rare Case of Atezolizumab-Induced Very Severe Aplastic Anemia.

Aplastic anemia is a rare bone marrow failure condition with pancytopenia and transfusion dependence. This condition is potentially fatal if left untreated. It is confirmed by bone marrow aspiration and biopsy showing diminished or absent hematopoietic precursors, with the severity of bone marrow failure ranging from non-severe to very severe based on the bone marrow cellularity and blood counts. This dreadful medical condition can be inherited, immune-mediated, or iatrogenic, with the latter category occurring due to direct damage to the hematopoietic stem and progenitor cells (HSPCs) in the bone marrow. The PD-L1 inhibitor atezolizumab is an immunotherapeutic medication that can cause aplastic anemia, albeit exceedingly rare, with only eight reports to date in the medical literature. We present a case of iatrogenic aplastic anemia from administration of the immune checkpoint inhibitor atezolizumab. This case report provides insight into the evaluation and management of very severe aplastic anemia secondary to atezolizumab and is, to our knowledge, the first reported case of iatrogenic aplastic anemia secondary to atezolizumab in an elderly female with non-small cell lung cancer (NSCLC).