Fluorodeoxyglucose Metabolic Phenotypes Across Molecular Subgroups of Primary Colorectal Cancer: A Retrospective Three-Group Analysis

Background/Objectives: Increased FDG uptake has been reported in RAS-mutant colorectal cancer (CRC), whereas the FDG metabolic phenotype of BRAF-mutant CRC is less well characterized. We compared FDG PET-derived parameters among RAS-mutant, BRAF-mutant, and RAS/BRAF double-wild-type primary CRCs and explored associations between mucinous components and FDG uptake within each subgroup. Methods: This retrospective study included 105 patients with 106 treatment-naive primary CRCs (44 RAS-mutant, 11 BRAF-mutant, and 51 double-wild-type tumors). Maximum standardized uptake value (SUVmax), peak standardized uptake value (SUVpeak), mean standardized uptake value (SUVmean), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) were measured. Mucinous components were assessed from original histopathological reports in 86 evaluable tumors. Results: SUVmax, SUVpeak, SUVmean, and TLG differed among the three subgroups (p = 0.006, 0.015, 0.009, and 0.039, respectively), whereas MTV did not (p = 0.130). After Bonferroni correction, RAS-mutant tumors had higher SUVmax, SUVpeak, and SUVmean than double-wild-type tumors. No significant pairwise differences involving BRAF-mutant tumors were observed. Mucinous components were present in 11/34 RAS-mutant, 4/10 BRAF-mutant, and 4/42 double-wild-type tumors (p = 0.015). In exploratory within-subgroup analyses, BRAF-mutant tumors with mucinous components had lower SUVmax, SUVpeak, and SUVmean than those without mucinous components (exact p = 0.010 for each; Bonferroni-adjusted p = 0.048 for each); no corresponding differences were observed in the other subgroups. Conclusions: RAS-mutant primary CRC showed higher metabolic intensity than RAS/BRAF double-wild-type CRC, whereas BRAF-mutant tumors did not differ significantly from either subgroup. The association between mucinous components and lower metabolic intensity in BRAF-mutant CRC should be considered exploratory and hypothesis-generating.