M+ dans 40 à 60% des cancers colo- rectaux

s, reports from meetings, editorial comments, and letters to the editor were excluded. CHEMOTHERAPY RESPONSE MONITORING IN ADVANCED COLORECTAL CANCER Tumor response to therapy is traditionally assessed by comparison of tumor sizes determined by morphologic imaging methods (CT) before and after treatment. According to the response evaluation criteria in solid tumors (RECIST), the current definition of tumor response is a decrease in the sum of the largest diameters of tumor lesions of at least 30% (8). The RECIST are widely accepted, but the correlation between morphologic tumor response and patient outcome is rather weak (9). Moreover, residual benign masses may persist, despite the fact that disease activity may have completely resolved after successful therapy. 18F-FDG PET yields data independent of associated structural characteristics and therefore allows the detection or monitoring of specific metabolic changes that are not associated with or that precede therapy-induced anatomic changes. The strength of 18F-FDG PET is that it permits whole-body imaging in a noninvasive way. In contrast to histopathologic analysis of biopsy material, 18F-FDG PET is not limited to the characterization of one or a few (sometimes very heterogeneous) target lesions; it can evaluate multiple tumor sites at the same time. Furthermore, serial scanning can be performed, allowing the measurement of functional changes over time during therapeutic interventions. PET not only can visualize (Fig. 1) but also can quantify 18F-FDG uptake and is able to provide several highly reproducible quantitative parameters of tumor glucose metabolism. However, the disadvantages of molecular imaging techniques (limited resolution and radiation burden) relative to techniques such as MRI should not be ignored. Therefore, these techniques should not be considered competitive but rather should be considered complementary because they aim to visualize and measure different processes in the human body. However, it is obvious that the introduction of targeted therapies, such as the angiogenesis inhibitor bevacizumab, requires new tools for monitoring therapeutic effects, because these agents exhibit a cytostatic effect rather than the cytoreductive effect of classic chemotherapy. These new agents inhibit the growth of new blood vessels in cancer tissue; this effect does not immediately lead to a decrease in tumor size and thus places new demands on imaging modalities. When anticancer treatment becomes more individualized, it is increasingly important to identify a response at earlier time points. Early identification of the lack of a response would prevent side effects, reduce the costs of futile treatment, and prevent delays in instituting a second-line, potentially effective, therapy. Five studies (Table 1) reported the predictive value of 18F-FDG PET in patients treated with chemotherapy for nonresectable colorectal cancer liver metastases (10–14). As early as 1996, Findlay et al. (10) studied 18 patients before, at 1–2 wk after, and at 4–5 wk after 5-fluorouracil (5-FU) chemotherapy with or without interferon-a by using a nondedicated PET system with a limited resolution. Responding lesions showed a significantly greater reduction in 18F-FDG uptake, compared with the baseline value, than nonresponding lesions (233% vs. 21%; P , 0.001). The 4to 5-wk tumor-to-liver ratio was able to discriminate responders from nonresponders in both a lesion-by-lesion assessment and an overall patient response assessment with a sensitivity of 100% and specificities of 90% and 75%, respectively. A clear correlation was observed between the reduction in tumor glucose metabolism at 5 wk after the start of chemotherapy and treatment outcome; such a correlation was not observed at 1–2 wk after the start of treatment. These results showed the importance of the correct timing of 18F-FDG PET after the beginning of chemotherapy. The authors mentioned the so-called flare phenomenon that occurs at 1–2 wk after the initiation of chemotherapy and that can be observed as a marked increase in 18F-FDG metabolism in lesions that show a