Conventional imaging methods such as CT and MRI are used to measure sarcoma patients’ responses to treatment by evaluating size changes in the tumors. If the size is reduced, a patient is said to have responded positively to the treatment. If the size doesn’t change, clinicians may discontinue or change the treatment. However, recent evidence has shown that assessing treatment response by measuring changes in tumor size may not be accurate.

As reported in the Feb. 1 issue of Clinical Cancer Research, Dr. Fritz C. Eilber from the University of California, Los Angeles, and his colleagues evaluated whether measuring changes in glucose metabolic activity using PET would provide a more accurate analysis of treatment response than the traditional size-based methods.

The researchers tested 42 patients with soft tissue sarcomas (connective tissue tumors) who were scheduled to undergo neoadjuvant therapy (chemotherapy before surgery). The patients received PET and CT scans with a Siemens Biograph duo PET/CT scanner before and after the therapy. Whole-body CT scans were taken first, followed by PET an hour after an injection of the glucose tracer FDG. For a standard comparison, all of the tumors were histopathologically analyzed. Patients with tumors that showed at least 95 percent necrosis (cancer cell death) were considered histopathologic responders to the neoadjuvant therapy.

Eight of the patients responded positively to the therapy, according to histopathology. Only two of these showed a decrease in tumor size of more than 30 percent in CT images — the amount classified as a positive treatment response, according to standard evaluation criteria. However, PET images revealed significant changes in metabolic activity in all eight patients. The changes in glucose metabolic activity were significantly more pronounced in the histopathologic responders than in the nonresponders.

The researchers conclude that FDG-PET is more accurate in assessing treatment response to neoadjuvant therapy than to size-based criteria methods and therefore recommend PET for monitoring patients with soft tissue sarcomas.