FDG-PET to evaluate response to hyperthermic isolated limb perfusion for locally advanced soft-tissue sarcoma

We investigated FDG-PET in patients undergoing hyperthermic isolated limb perfusion (HILP) with rTNF-alpha, rIFN-gamma and melphalan for locally advanced soft-tissue sarcoma of the extremities.

Twenty patients (11 women, 9 men; aged 18-80 yr, mean age 49 yr) were studied. FDG-PET studies were performed before, 2 and 8 wk after HILP. After the final PET study, the tumor was resected and pathologically graded. Patients with pathologically complete response (pCR) showed no viable tumor after treatment. Those with pathologically partial response (pPR) showed various amounts of viable tumor in the resected specimens.

Seven patients showed a pCR (35%) and 12 patients showed a pPR (60%). In one patient, pathological examination was not performed (5%). The pre-perfusion glucose consumption in the pCR group was significantly higher than in the pPR group (p<0.05). Visual analysis of the PET images after perfusion showed a rim of increased FDG uptake around the core of absent FDG uptake in 12 patients. The rim signal contained a fibrous pseudocapsule with inflammatory tissue in the pCR group, viable tumor was seen in the pPR group. The glucose consumption in the pCR group at 2 and 8 wk after perfusion had decreased significantly (p<0.05) in comparison to the glucose consumption in the pPR.

Based on the pretreatment glucose consumption in soft-tissue sarcomas, one could predict the probability of a patient achieving complete pathological response after HILP. FDG-PET indicated the pathological tumor response to HILP, although the lack of specificity of FDG, in terms of differentiation between an inflammatory response and viable tumor tissue, hampered the discrimination between pCR and pPR.