The use of PET in assessing tumor response after neoadjuvant chemoradiation for rectal cancer

Purpose: To assess the correlation of 18F-FDG-PET (PET) response to pathological response after neoadjuvant chemoradiation (CRT) for locally advanced rectal cancer. Methods and materials: Twenty patients with locally advanced rectal cancer were identified between 2001 and 2005. The median age was 57 years (range 37-72) with 14 males and 6 females. All patients were staged with endorectal ultrasound and/or MRI, CT, and PET. The clinical staging was T3N0M0 (16), T3N1M0 (2), and T3N0M1 (2). Restaging PET was performed after CRT, and prior to definitive surgery. The response on PET and pathology was assessed and correlated. Patient outcome according to PET response was also assessed. Results: Following CRT, a complete PET response occurred in 7 patients, incomplete response in 10, and no response in 3 patients. At surgery, complete pathological response was recorded in 7 patients, incomplete response in 10 and no response in 3. There was a good correlation of PET and pathological responses in complete responders (5/7 cases) and non-responders (3/3 cases). After a median follow-up of 62 months (range 7-73), twelve patients were alive with no evidence of disease. All patients achieving complete metabolic response were alive with no evidence of disease, while as those who had no metabolic response, all died as a result of metastatic disease. Conclusions: PET is a promising complementary assessment tool for assessing tumor response after CRT if there is a complete or no response. PET response may also predict for outcome.