FDG PET/CT reveals necrotic nuances in sarcomas that predict survival

Little improvement in survival has been made for patients with sarcomas, despite an array of aggressive treatments. Researchers are trying to identify patients at high risk of recurrence by performing FDG PET/CT to quantify necrotic areas of tissue, a strong indicator of survival, according to research published in the July issue of the American Journal of Roentgenology.

Rajan Rakheja, MD, at the department of Nuclear Medicine, Royal Victoria Hospital in Montreal, Canada, and colleagues conducted a study to gauge the relationship between necrosis at staging of sarcomas and both overall survival (OS) and progression-free survival (PFS).

“Tumor necrosis has been repeatedly shown to be an important prognostic factor in soft-tissue sarcomas with respect to overall and metastasis-free survival,” wrote Rakheja et al. “New prognostic models (e.g., the SING [size, invasion, necrosis, growth] model) have been proposed that include necrosis as one of the main variables.”

Sarcomas are relatively rare in the general population, about 0.7 percent of all adult malignant cancers, but they  account for about 6.5 percent of childhood cancers and have a high mortality rate, leading to 3 to 4 percent of overall cancer deaths. Necrosis could be a way forward to better stratify patients, but a very high level of interobserver variation exists. In fact, there may be no more than 60–70 percent concordance between well trained clinicians. This research indicates necrosis, or hypometabolism within a hypermetabolic tumor, can be better quantified with FDG PET/CT, potentially improving patient management for those at increased risk of recurrence.

For this study, 66 patients with a median age of 49 years with newly diagnosed limb and girdle sarcoma were staged for treatment with FDG PET/CT between June 2004 and July 2009. Researchers calculated tumor necrosis, volume of necrosis and maximum standardized uptake values (SUVmax), the presence of necrosis and the volume of necrosis. Results were correlated with PFS and OS at a mean follow up of just over 33 months by Kaplan-Meier analysis. Follow up showed that 53 percent of patients had progressive disease and about 40 percent of patients had died. Necrosis was significantly related to poor survival. Patients with no necrosis were shown to have 96 percent OS at 24 months, those with some necrosis had 65 percent OS and those with greater than 50 percent necrosis had 38 percent OS. At 48 months it was whittled down to 81 percent for necrosis-free patients and 41with some necrosis. PFS at 12 months was found to be 96 percent, 60 percent and 42 percent for no necrosis, some necrosis and greater than 50 percent necrosis, and at 24 months was pinched to 83 percent, 38 percent and 22 percent, respectively.

“Further quantifying the amount of necrosis on PET/CT appears to enhance the prognostic potential,” wrote the authors. “These metabolic markers could aid in clinical decision making before surgery and could help in risk stratification to optimize treatment of this very heterogeneous group of tumors.”