OA170] Myelosuppression in non–hodgkin lymphoma patients treated with 177Lu-lilotomab satetraxetan can be predicted by a model with red marrow absorbed dose as the only parameter

Abstract

Purpose 177Lu-lilotomab satetraxetan is an antibody-radionuclide conjugate therapy for non–Hodgkin lymphoma, which is currently in a phase 1/2-study. The primary toxicity is transient myelosuppression. The aim of this work was to determine if a linear model including red marrow absorbed dose and various clinical factors can be used to predict myelosuppression. Methods Patient characteristics and dosimetric data for 17 patients were included. All patients had no or minor bone marrow infiltration. The percentage reduction of neutrophils and platelets at nadir compared to baseline was used as to indicate myelosuppression. Platelets and neutrophils were analysed separately. The Common Terminology Criteria version 4.0 were used to grade thrombocytopenia and neutropenia. A total of six factors believed to affect bone marrow reserve were tested: Red marrow absorbed dose, age at treatment, baseline cell-counts, history of prior external beam radiation therapy, total number of previous chemotherapy treatments (including rituximab) and elapsed time since the last chemotherapy treatment. Predictors were found using ordinary least square fitting, testing all possible subsets of variables. A significance level of 0.05 was used. A leave 1-out analysis was used to validate the final model. Results The typical patient, as described by the mean and standard deviation, was 69 (+/−10) years of age at treatment, had previously been treated 2.8 (+/−1.8) times with chemotherapy and might have previously received external beam radiation therapy (5/17 patients). Elapsed time since the last chemotherapy was 20.9 (+/−17.2) months. Mean red marrow absorbed dose was 1.45 (+/−0.45) Gy. Of the sub-sets of predictors investigated, only a model consisting solely of the red marrow absorbed dose was significant (p = 0.048 for platelets and 0.027 for neutrophils). Model coefficients indicate total loss of both platelets and neutrophils at 3 Gy. The leave-1 out analysis resulted in correct prediction of CTCAE-grading +/−1 grade for 76.5 % (13/17) and 88.2 % (15/17) of the patients for thrombocytopenia and neutropenia, respectively. Conclusions A linear model with red marrow absorbed dose as the only parameter predicted myelosuppression in 177Lu-lilotomab satetraxetan treated patients.