Outcomes of adults with lymphoma treated with nonmyeloablative TLI-ATG and radiation boost to high risk or residual disease before allogeneic hematopoietic cell transplant.

We evaluated the impact on survival of antithymocyte globulin conditioning (TLI-ATG) with radiation (RT) boost to high risk or residual disease before allogeneic hematopoietic cell transplant (allo-HCT) for adults with lymphoma (excluding mycosis fungoides and low-grade NHL other than SLL/CLL). Of 251 evaluable patients, 36 received an RT boost within 3 months of allo-HCT at our institution from 2001 to 2016. At the time of TLI-ATG, patients who received boost vs no boost had a lower rate of CR (11% vs 47%, p = 0.0003), higher rates of bulky disease (22% vs 4%, p < 0.0001), extranodal disease (39% vs 5%, p < 0.0001), and positive PET (75% vs 28%, p < 0.00001). In the boost group, the median (range) largest axial lesion diameter was 5.2 cm (1.8-22.3). Median follow-up was 50.2 months (range: 1-196). There was no significant difference in OS, time to recurrence, or time to graft failure with vs without boost. A trend toward higher percent donor CD3+ chimerism was seen with vs without boost (p = 0.0819). The worst boost-related toxicity was grade 2 dermatitis. RT boost may help successfully mitigate the risk of high risk or clinically evident residual disease in adults with lymphoma undergoing allo-HCT.