Long-term follow-up for the development of subsequent malignancies in patients treated with genetically modified IECs

Subsequent malignancies are well-documented complications in long-term follow-up of cancer patients. Recently, genetically modified immune effector cells (IECs) have showed benefit in hematologic malignancies and are being evaluated in clinical trials for solid tumors. While the short-term complications of IECs are well described, there is limited literature summarizing long-term follow-up, including subsequent malignancies. We retrospectively reviewed data from 340 patients treated across 27 investigator-initiated pediatric and adult clinical trials at our center. All patients received IECs genetically modified with gamma-retroviral vectors to treat relapsed and/or refractory hematologic or solid malignancies. In a cumulative 1,027 years of long-term follow-up, 13 patients (3.8%) developed another cancer with a total of 16 events (four hematologic malignancies and 12 solid tumors). The 5-year cumulative incidence of a first subsequent malignancy in the recipients of genetically modified IECs was 3.6% (95% CI: 1.8%-6.4%). For 11 of the 16 subsequent tumors, biopsies were available, and no sample was transgene positive by PCR. Replication competent retrovirus testing of peripheral blood mononuclear cells was negative in the 13 patients with subsequent malignancies tested. Rates of subsequent malignancy were low and comparable to standard chemotherapy. These results suggest that the administration of IECs genetically modified with gamma retroviral vectors does not increase the risk for subsequent malignancy.