Previously, we developed a complete human IgG TFR1 antibody (JST-TFR09/PPMX-T003) that showed a potentially practical therapeutic effect against adult T-cell leukemia/lymphoma (ATLL) in vitro and in vivo. In the present study, to elucidate the molecular mechanism underlying ATLL cell death induced by anti-TFR1 antibodies, we performed comprehensive gene expression analysis and mass spectrometry on ATLL cells treated with PPMX-T003 antibody. These results suggest that PPMX-T003 antibody treatment of ATLL cell lines induces ferroptosis mediated by ferritin degradation. PPMX-T003 antibody-treated ATLL cell lines showed a decrease in ferritin proteins, an increase in ferrous iron (Fe