Clinical impact of 18F-FDG PET/MR in treated colorectal cancer patients

214 Objectives: Despite treatment advancements, colorectal cancer (CRC) still represents the second cause for cancer death worldwide. Preliminary studies have shown that 18F-FDG PET/RM might outperform 18F-FDG PET/CT and contrast enhanced CT in CRC staging, allowing a more accurate local and distant staging. Our primary outcome of interest was to determine whether 18F-FDG PET/MR can change the clinical management of patients with treated CRC in relation to standard care of imaging (SCI). Methods: Treated CRC patients who underwent 18F-FDG PET/MR were enrolled in this retrospective observational diagnostic study. The eligible inclusion criteria were patients who performed PET/MR for treated CRC due to suspicion for recurrence by CEA elevation and/or indeterminate findings in other imaging studies (CT and/or MRI). All patients underwent a whole body 18F-FDG PET/MR. Images were collected about 1.5 h following a mean dose of 4.44 MBq/kg (0.12 mCi/kg) of FDG injection. All patients underwent a combination of standard care of imaging (SCI): chest, abdominal and pelvic contrast-enhanced CT, and/or 18F-FDG PET/CT, and/or abdominal or pelvic enhanced MRI. The original 18F-FDG PET/MR and SCI reports and the patient´s electronic medical records were evaluated to ascertain if any change in management had been prompted by PET/MR versus SCI. Differences between PET/MR and the SCI were classified as no change, when the standard care of imaging and PET/MR led to same oncologic conduct and change in management when PET/MR led to a change in the oncologic management. A secondary outcome of interest was analyzing the staging performance of PET/MR versus that of SCI. Exact McNemar’s chi-squared test was used to ascertain if the differences were statistically significant. Results: A total of 39 patients with 42 studies were included, mean age 56.7 years, 26 males. PET/MR did not change clinical management, in comparison with the SCI, in 27/42 (64%) cases. PET/MR prompted changes in management in 15/42 cases (36% of cases), especially due to upstaging (9/15 or 60%). Changes in management were distributed as follow: upstaging prompting surgery in 5/15 (33.3%); upstaging aborting surgery in favor of chemotherapy in 2/15 (13.3%) and in favor of chemoradiotherapy combined with immunotherapy in 2/15 (13.3%); downstaging making patients resectable in 5/15 (33.3%); downstaging avoiding unnecessary surgery in 1/15 (6.8%). There was statistically significant difference between the management prompted by SCI and PET/MR, in favor of PET/MR (P-value = 0.0000685; odds radio = 9.75 +/- 1.27). In relation to the secondary outcome, PET/MR outperformed the SCI in oncologic staging. The main difference was due to upstaging achieved by PET/MR, showing lesions that were not detected by the SCI. The McNemar´s chi-squared test was statically significant (P-value = 0.01586). Conclusion: Only few studies have investigated the utility of PET/MR in CRC patients. The majority of them have demonstrated the superiority of PET/MR in relation to other imaging modalities. Our study showed that 18F-FDG PET/MR can change the oncologic management in about one-third of treated CRC patients. This is the result of a better staging than achievable by standard care of imaging. Multicenter prospective studies with larger patient sample might be useful to confirm these preliminary results.