Relationship Between 18F-Fluorodeoxyglucose Uptake and V-Ki-Ras2 Kirsten Rat Sarcoma Viral Oncogene Homolog Mutation in Colorectal Cancer Patients: Variability Depending on C-Reactive Protein Level.

To evaluate clinical values of clinicopathologic and 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT)-related parameters for prediction of v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) mutation in colorectal cancer (CRC) and to investigate their variability depending on C-reactive protein (CRP) levels. In total, 179 CRC patients who underwent PET/CT scans before curative resection and KRAS mutation evaluation following surgery were enrolled. Maximum standardized uptake value (SUV max), peak standardized uptake value (SUV peak), metabolic tumor volume, and total lesion glycolysis were determined semiquantitatively. Associations between clinicopathologic and PET/CT-related parameters and KRAS expression were analyzed. Elevated CRP (> 6.0 mg/L; n = 47) was associated with higher primary tumor size, higher SUV max, SUV peak, metabolic tumor volume, and total lesion glycolysis, compared with those for the group with a CRP lower than that the cutoff value (< 6.0 mg/L; n = 132). Interestingly, the CRC patients (having CRP < 6.0 mg/L) with KRAS mutations had significantly higher (P < 0.05) SUV max and SUV peak values than the patients expressing wild-type KRAS mutations. Multivariate analysis revealed SUV max and SUV peak to be significantly associated with KRAS mutations (odds ratio = 3.3, P = 0.005, and odds ratio = 3.9, P = 0.004), together with histologic grade and lymph node metastasis. 18F-FDG uptake was significantly higher in CRC patients with KRAS mutations and with normal CRP levels. A severe local inflammation with raised CRP levels, however, might affect accurate 18F-FDG quantification in CRC tumors. Positron emission tomography/computed tomography-related parameters could supplement genomic analysis to determine KRAS expression in CRC; however, care should be exercised to guarantee proper patient selection.