Development of Acute Adult T-cell Leukemia Following PD-1 Blockade Therapy for Lung Cancer

Immune checkpoint inhibitors (ICIs) are widely used for the treatment of various cancers. However, paradoxical exacerbation of neoplasms, referred to as "hyperprogressive disease," has been reported in a proportion of patients treated with anti-programmed cell death-1 (PD-1)/PD-1 ligand (PD-L1) blockade. We herein report a case of acute adult T-cell leukemia (ATL) that developed shortly after the administration of nivolumab, a PD-1 inhibitor, to treat non-small-cell lung cancer. There were no signs of ATL before the administration of nivolumab, and seropositivity for human T-cell leukemia virus type-1 (HTLV-1) was confirmed after the development of acute ATL. We speculate that nivolumab likely contributed to the development of acute ATL.