Imaging marrow cell population change in lymphoma after chemotherapy by FDG-PET scans and its clinical implications

Abstract

Purpose: It is common to see the pattern of diffusely increased FDG uptake in normal bone marrow after chemotherapy on FDG-PET scans due to change in hematopoietic cell population. Decreased FDG uptake after chemotherapy is noted in the areas with PET evidence of bone marrow involvement due to reduction in tumor population. The aims were to correlate cell population change with SUV change over bone marrow biopsy (BMBx) sites after chemotherapy using bone marrow histopathology as the gold standard and investigate its potential predictive value for occult bone marrow involvement by malignant lymphoma. Methods: 26 patients (mean age, 58±15y; 13 female, 13 male) with follicular lymphoma (FL) (Grade I, II, III, n=16) or diffuse large B-cell lymphoma (DLBC) (n=10), referred for FDG-PET/CT scan for initial staging and first restaging after chemotherapy, who had BMBx from unilateral or bilateral iliac crest(s) before chemotherapy, were studied retrospectively. The maximal standardized uptake value (SUV) was measured from BMBx site over the same area on both initial staging and restaging FDG-PET/CT scans. The interval changes of SUV were classified as increase or decrease and correlated with BMBx result of positive or negative for bone marrow involvement by lymphoma. Results: 35 BMBx sites in 26 patients were evaluated. 12 of 35 sites were BMBx positive with interval decrease in SUV in 11 of 12 sites (92%). The remaining 23 of 35 sites were BMBx negative with interval increase in SUV in 21 of 23 sites (91%). The correlation between SUV change over the BMBx site before and after chemotherapy and BMBx result was significant (P<0.0001). Among 14 of the 26 patients (FL, n=4; DLBC, n=10) with focal increased FDG uptake (SUV range form 4.3-31.9) in bone marrow indicating involvement by lymphoma on initial staging scans, all (100%) showed significant interval decreased SUV after chemotherapy. Conclusions: This study demonstrates a strong correlation between marrow metabolic changes (as determined by FDG PET) after chemotherapy with marrow cell population change. This may provide a retrospective means of predicting occult marrow involvement and may help in deciding to deliver more extended therapy during management of lymphoma patients.