PET/CT and histopathologic response to preoperative chemoradiation therapy in locally advanced rectal cancer

PURPOSE: The objective of this study was to investigate the possibility of using positron emission tomography/computer tomography to predict the histopathologic response in locally advanced rectal cancer treated with preoperative chemoradiation. METHODS: The study included 30 patients with locally advanced rectal adenocarcinoma treated with a combination of radiotherapy and concurrent Uftoral(R) (uracil, tegafur) and leucovorine. All patients were evaluated by positron emission tomography/computer tomography scan seven weeks after end of chemoradiation, and the results were compared to histopathologic tumor regression as the standard. The pathologic response was quantified by tumor regression grade. RESULTS: Positron emission tomography/computer tomography correctly identified six of eight patients (specificity 75 percent) with complete pathologic response. However, the sensitivity of positron emission tomography/computer tomography was only 45 percent and the accuracy 53 percent. The positive and negative predictive values were 83 and 33 percent, respectively. CONCLUSIONS: We conclude that positron emission tomography/computer tomography performed seven weeks after the end of chemoradiation is not able to predict the histopathologic response in locally advanced rectal cancer. There is an obvious need for other complementary methods especially with respect to the low sensitivity of positron emission tomography/computer tomography.