RSNA: FLT bests FDG for differentiating benign and malignant tumors in uterus

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CHICAGO—18F-FLT PET presented much higher specificity than 18F-FDG PET for detecting uterine malignant tumor, and FLT PET correlated to cell proliferation better than FDG PET, based on a small Japanese study presented Nov. 29 at the 97th Scientific Assembly and Annual Meeting of the Radiological Society of North America (RSNA).

Uterine leiomyoma, common benign smooth muscle tumor, occasionally resembles malignant tumor, such as leiomyosarcoma and uterine corpus cancer.

In this study, Tomohiko Yamane, MD, and colleagues from Daiyukai General Hospital in Aichi, Japan, sought to investigate the efficacy of 18F-FLT PET for differentiating uterine leiomyoma from malignancy in comparison with 18F-FDG PET. 

The study enrolled 15 patients (26 to 65 years old, median age 44 years) with uterine corpus tumor which had the possibility of being leiomyosarcoma by clinical findings. None of them had the evidence of carcinoma by transvaginal cytology or biopsy prior to PET scans.

Both FLT and FDG PET were performed, and the researchers measured each maximum standardized uptake value (SUVmax). In case surgical resection was performed after the PET scans, SUVmax of each tracer was compared with Ki-67 labeling index to elucidate the relationship to cell proliferation. 

Surgical resection was performed in 13 cases, and four cases were diagnosed with malignancy (uterine leiomyosarcoma in two cases and corpus carcinoma in two cases). The other nine cases were diagnosed with benign leiomyoma. In addition, two cases were also diagnosed with benign leiomyoma by follow-up at least for six months. Overall, a total of 13 cases were diagnosed with benign leiomyoma.

The cut-off SUVmax to detect malignancy was estimated to be 2.1 on FLT PET and 4.3 on FDG PET by receiver operating characteristic analysis, Yamane reported. At the cut-off value, sensitivity and specificity were 100 percent and 89 percent in FLT PET, and 100 percent and 67 percent in FDG PET, respectively.

The researchers conducted a comparison of SUVmax between benign and malignant by means of Wilcoxon signed-rank test, which revealed significant in FLT PET, and not significant in FDG PET. SUVmax of FLT PET was correlated to Ki-67 labeling index better than SUVmax of FDG PET ( R2 = 0.89 vs. 0.35). 

“Negative findings on additional FDG PET or FLT PET may deny the possibility of malignancy for patients with suspected leiomyosarcoma,” Yamane said. “However, leiomyosarcoma with severe necrotic tissue has the possibility of false negative diagnosis.”

According to Yamane and his colleagues, this study indicated that FLT PET had the possibility of becoming a valuable diagnostic tool for differentiating benign uterine leiomyoma, which clinically resembles malignancy, from malignant uterine tumor. 

Commenting on the study, Steven M. Larson, MD, chief of nuclear medicine services at Memorial Sloan-Kettering Cancer Center in New York City, who called the study “excellent," said these findings “highlight both the potential and problem with FLT because it’s greatest use is going to be in those tumors where you can isolate the tumor from the normal tissue.”