Severe Autoimmune Hemolytic Anemia After Pembrolizumab for Metastatic Lung Cancer

What happened, in summary

A 69-year-old man with a history of smoking was diagnosed in February 2024 with Stage IV lung adenocarcinoma that had spread to the left adrenal gland and a subdiaphragmatic site. Tumor testing showed high PD-L1 expression at 70%, and he started pembrolizumab alone with palliative intent.

Less than 2 weeks after the first dose, he developed worsening jaundice, dark stools, severe fatigue, and light-headedness. He arrived at the hospital with profound anemia and laboratory findings showing rapid destruction of red blood cells. The pattern was consistent with autoimmune hemolytic anemia triggered by pembrolizumab.

He was treated urgently with intravenous immunoglobulin, high-dose steroids, and several red-blood-cell transfusions. His hemolysis improved quickly, his bilirubin fell, and his hemoglobin stabilized. He was discharged after 5 days on a 6-week steroid taper, with continued hematology and oncology follow-up.

Because the reaction was life-threatening, pembrolizumab was permanently stopped. Because the reaction was life-threatening, pembrolizumab was permanently stopped, changing the planned cancer-treatment course.