Features of large cell transformation of indolent lymphomas as observed on sequential PET/CT

Detection of large cell transformation (LCT) has been reported with the increasing use of PET/computed tomography (CT) in patients with indolent lymphomas. However, there is little information on PET/CT characteristics, specifically, the distribution of lesion maximum standardized uptake value (SUV(max)) within a patient, or SUV(max) changes before and after LCT. Our objectives were to compare SUV(max) values and distribution between nontransformed and LCT patients; to compare SUV(max) of LCT and nontransformed lesions in patients with documented focal transformation; and to measure the SUV(max) changes in patients before and after LCT.

Retrospective study of patients with LCT (n=29)compared with nontransformed (n=41), and comparison of LCT and nontransformed lesions within patients and over time.

On average, the highest SUV(max) was greater in LCT patients than in nontransformed patients. In addition, there was a wider range of SUV(max) values in the LCT group compared with the nontransformed group (P<0.05). The median ratio of the SUV(max) of 12 LCT to nontransformed biopsy-proven lesions in the same patient was 4.3, P value of less than 0.05 (range 2.6-15.5). In 10 of 12 patients it was greater than or equal to 3. No change in highest SUV(max) and distribution was shown on serial PET in untreated nontransformed patients.

LCT is often focal and is associated with higher SUV(max) than nontransformed. The emergence of a focus with SUV(max) three times or higher than others on a single scan, or that has tripled or more in value on serial scans, should raise suspicion for LCT.