Is there a correlation between tumor proliferative activity and the FDG phenotype in pediatric sarcomas?

Objectives Pediatric soft tissue and bone sarcomas exhibit a strong glycolytic phenotype by 18FDG PET/CT. Here we investigate whether there is a correlation between tumor SUV and the tumor tissue proliferation marker Ki-67.

Methods The study included 22 pediatric patients with high grade soft tissue or bone sarcomas. Fifteen (68%) patients underwent PET/CT scans while 7 (32%) had a dedicated PET. Tumor FDG uptake was quantified by SUVmax and tumor to liver ratios (SUVratio). Immunohistochemical staining for Ki-67 with MIB-1 was performed on previously biopsied tissue of all tumors.

Results There were 22 patients (17 males, 5 females; mean age 14±5.0 years), 15 of which had bone sarcomas (osteosarcoma: n=8; Ewing’s sarcoma: n=7), and seven had soft tissue sarcomas. The tumors were localized in the extremities (n=15) or the abdomen/pelvis (n=7). SUVmax ranged from 1.6 to 20.4 (median 4.9) in bone sarcomas and 1.4 to 5.3 (median 2.3) in soft tissue sarcomas. A significant correlation between SUVmax and tumor Ki-67 expression was observed for the entire group (r2=0.48; p<0.001). However, a subgroup analysis revealed that this correlation was only significant in bone sarcomas (r2=0.62; p<0.001) but not in soft tissue sarcoma (r2=0.01; p=0.8). Similarly, the SUV ratio correlated with Ki-67 tumor expression for the entire study group (r2=0.32; p=0.006), for bone sarcomas (r2=0.45; p=0.006) but not for soft tissue sarcomas (r2=0.03; p=0.7).

Conclusions The expression of Ki-67 correlates with the FDG uptake in pediatric bone sarcomas but not in soft tissue sarcomas suggesting that the degree of FDG uptake provide information about tumor proliferative activity only in bone but not in soft tissue sarcoma. The reasons for the lack of correlation in soft tissue sarcomas await further clarification