Imaging of soft-tissue tumors using L-3-[iodine-123]iodo-alpha-methyl-tyrosine single photon emission computed tomography: Comparison with proliferative and mitotic activity, cellularity, and vascularity

The radiolabeled amino acid L-3.[I-123]-iodo-alpha-methyl-tyrosine (IMT) is a new tumor tracer that accumulates in many tumors and is suitable for sin gle photon emission computed tomography (SPECT) imaging. Using IMT SPECT, w e studied 32 patients with a soft-tissue tumor suspected to be a soft-tissu e sarcoma to determine whether: (a) tumors can be visualized; (b) benign an d malignant lesions can be distinguished; and (c) IMT uptake is related to tumor grade and proliferation. Whole-body imaging was performed 15 min afte r administration of 300 MBq IMT, biopsy, or resection 1-2 weeks later, IMT uptake was quantified using a region-of-interest method resulting in tumor: background (T:B) ratios. These were compared with tumor grade, mitotic inde x, tumor cellularity, vascularity, and the Ki-67 proliferation index. Eleve n patients had a benign tumor, and 21 patients had a soft-tissue sarcoma, S ix benign tumors demonstrated minor IMT uptake, and five lipomas had no upt ake. All malignant tumors had high uptake and were clearly visualized. T:B ratios in malignant tumors (3.83 +/- 1.16) were higher (P < 0.001) than in benign tumors (152 +/- 0.60). Small (<5 mm) metastases in two patients were not detected, Taking the T:B ratio 2.0 as the cutoff level, the sensitivit y for detection of malignancy was 100%, and specificity was 88%. IMT uptake correlated with histological grade (r = 0.82; P < 0.001), mitotic index (r = 0.75; P < 0.001), tumor cellularity (r = 0.73; P < 0.01), and with the K i-67 proliferation index (r = 0.63; P < 0.01). In conclusion, IMT SPECT vis ualized all soft-tissue sarcomas, Uptake in sarcomas was clearly higher tha n in benign lesions yielding 100% sensitivity for detection of malignancy a t 88% specificity, Uptake increased with higher tumor grade and higher prol iferation rate.