Subsequent cancers following non-myeloablative conditioning for allogeneic hematopoietic cell transplantation.

We examined the risk of subsequent malignant neoplasms (SMNs) in 1720 patients with hematologic cancers given allogeneic hematopoietic grafts from 03/1998 to 08/2023 after nonmyeloablative conditioning regimens. With a median follow-up of 12 years, the cumulative incidence of SMNs was 17% (95% CI, [15%, 19%]). Most SMNs (n = 543) were non-melanoma skin cancers seen in 208 patients; unfortunately, information on these cancers was not available in the Surveillance, Epidemiology, and End Results (SEER) database for comparison with such tumors in the general population. However, developing non-melanoma skin cancers was statistically significantly associated with chronic GVHD and, thus, unlikely to be conditioning regimen related. Eighty-six patients (5%) developed 93 other SMNs. This number (93 SNMs) significantly exceeded the expected 73.4 cases in the comparison group (p = 0.03). This increase was driven exclusively by increases in uterine adenocarcinoma (n = 2), squamous lip cancer (n = 5), and squamous penile cancer (n = 2); the latter two cancers were, again, associated with chronic GVHD. Apart from these three tumor types, there were no observed increases in the risk of other tumors compared to those in the general population.