pet evaluation of response after 1 course of chemotherapy as predictor of treatment outcome.

Conditions: Colorectal Cancer Metastatic; Early Response Evaluation; Fdg-PET

Summary: study hypothesis : early decrease in fdg-pet measured suv max after 1 cycle of chemotherapy can accurately predict response of chemotherapy as assessed by conventional radiology after 3 cycles of chemotherapy. fdg-pet imaging will be done at j0 and j14 of a new line of chemotherapy treatment in metastatic colorectal cancer. suv max will be recorded and delta suvmax will be compared to the results of conventional radiological evaluation after 3 courses of chemotherapy. results will also be compared to the time to disease progression.

statistical hypothesis : sample size calculation for fdg-pet in metastatic patients. in the paper of cascini et al. \[1\], they have 18 patients with a trg response (trg = tumor regression grade) and 15 patients with no response. suv mean was measured at baseline and at day 12 in all 33 patients. all 33 patients showed a reduction in suv-mean from baseline to day 12. the median reduction in suv-mean was 63% (mean 66%) in responding tumors and 22% (mean 22%) for non responding tumors. using a cutoff level of 52% a perfect accuracy could be obtained, i.e. all responding tumors had a suv-mean reduction higher than 52% and all non responding tumors had a suv-mean reduction lower than 52%. (standard deviation of the suv-mean reduction was 25.) all 33 patients showed also a reduction in suv-max from baseline to day 12. the median reduction in suv-max was 62% in responding tumors and 28% in non responding tumors. (no information about mean or standard deviation of suv-max available in \[1\].) based on the data of suv-mean we can do a power calculation based on the wilcoxon test: in order to demonstrate an absolute difference in the mean of δsuv-mean of 44% between responding and non responding patients, with an estimated standard deviation of 25, using 35 patients (50% response, 50% no response), at a significance level of 5%, we obtain a power of 0.98. for suv-max, if we assume that the difference in the means is similar to the difference in the medians, i.e. 34% and the standard deviation is similar to the one of suv-mean, i.e. 25, we obtain a power of 0.93 if we, to be safe, are a little bit less optimistic and estimate that the difference in the mean of δsuv-max between responding and non responding tumors would be a little lower than in \[1\]: 35%, and the standard deviation a little bit higher: 30, then we need 40 patients at a power of 0.90 référence 1 : cascini gl, avallone a, delrio p, guida c, tatangelo f, marone p et al.: f-18-fdg pet is an early predictor of pathologic tumor response to preoperative radiochemotherapy in locally advanced rectal cancer. journal of nuclear medicine 2006, 47: 1241-1248.

Eligibility criteria:
inclusion criteria: * advanced colorectal cancer * evaluable disease * signed informed consent exclusion criteria: * no other cancer * no other life-threatening condition * unwillingness or inability to sign informed consent * active cerebral metastasis

Keywords: metastatic colorectal cancer fdg pet response evaluation