HTLV-1 seropositive patients with lung cancer treated with PD-1 inhibitors.

Adult T cell leukemia-lymphoma (ATL) is a peripheral T cell malignancy caused by human T cell leukemia virus-type 1 (HTLV-1).1 Frequent structural variations that disrupt the 3' untranslated region of the programmed cell death-ligand 1 (PD-L1) gene have been found to result in overexpression of PD-L1 in ATL patients.2 The programmed cell death-1 (PD-1)-PD-L1 axis has thus attracted attention as a potential therapeutic target for ATL. However, in a phase 2 trial of the PD-1 inhibitor nivolumab in ATL patients with an increased mutational load and overexpression of PD-L1, the first three patients unexpectedly developed rapid progression of disease after a single dose of nivolumab.