The relationship between clinical and pathological findings and FDG - PET uptake in metastatic colorectal cancers.

Background: In metastatic colorectal cancer (mCRC), the genetic structure and cell metabolism of the primary tumor lesion might be different from metastatic lesions. It is thought that cell-level glucose metabolism may differ due to the difference in RAS wild and mutant mCRC patients' prognosis. In this study, we aimed to compare 2-deoxy-2-[fluorine-18]-fluoro-D-glucose Positron Emission Tomography (18F-FDG PET/CT) uptake levels for KRAS mutation status and primary-metastatic tumor localization.

Methods: Our study is a retrospective cohort analysis that included RAS mutation status study and staging-oriented 18F-FDG PET/CT conducted on mCRC patients.

Results: There was no significant relationship between metastasis and primary tumor maximum Standardized uptake value (SUVmax) values according to the KRAS mutational status (P > 0.05). Patients with liver metastasis along with mutant BRAF mutation status had significantly higher SUVmax values in PET-CT scans (P = 0.04). There was a negative correlation between SUVmax values of lung metastases and overall survival (r = -0.35, P = 0.04). Patients with high carcinoembryonic antigen (CEA) levels had significantly higher SUVmax values of lung metastasis than patients with normal CEA levels (P = 0.009). Patients with high CA19-9 levels had significantly higher SUVmax values of liver, peritoneal, and bone metastasis than patients with normal CA19-9 levels (P = 0.002, P = 0.001, P = 0.004, respectively). There was no significant correlation between SUVmax values of metastasis and Lactate dehydrogenase (LDH) values. Liver metastasis of right-sided mCRCs had significantly higher SUVmax values (P = 0.03).

Conclusion: We could not demonstrate a significant association between KRAS mutation and SUVmax values of PET scan in primary or metastatic tumor sites in advanced CRC.