Relationship Between ¹⁸F-FDG PET/CT Scans and <i>KRAS</i> Mutations in Metastatic Colorectal Cancer

Several studies have shown that <i>KRAS</i> mutations in colorectal cancer (CRC) result in the lack of response to anti-epidermal growth factor receptor–based therapy; thus, <i>KRAS</i> mutational testing has been incorporated into routine clinical practice. However, 1 limitation of this test is the heterogeneity of <i>KRAS</i> status, which can be either intratumoral heterogeneity within an individual primary CRC or discordant <i>KRAS</i> status between a primary CRC and its corresponding metastases. We previously reported that ¹⁸F-FDG accumulation was significantly higher in primary CRCs with mutated <i>KRAS</i> than in those with wild-type <i>KRAS</i>. However, the clinical utility of the previous report has been limited because endoscopic biopsy for testing <i>KRAS</i> status is safe and feasible only in primary CRC. The purpose of this study was to investigate whether <i>KRAS</i> status is associated with ¹⁸F-FDG accumulation in metastatic CRC and whether ¹⁸F-FDG PET/CT scans can be used to predict the <i>KRAS</i> status of metastatic CRC. <b>Methods:</b> A retrospective analysis was performed on 55 metastatic CRC tumors that were identified by ¹⁸F-FDG PET/CT before surgical resection. Maximum standardized uptake value (SUV_max) of the respective metastatic tumor was calculated from ¹⁸F-FDG accumulation. <b>Results:</b> From the analysis with the 55 tumors, no significant correlation was found between SUV_max and <i>KRAS</i> status. We next analyzed only tumors larger than 10 mm to minimize the bias of partial-volume effect and found that SUV_max was significantly higher in the <i>KRAS</i>-mutated group than in the wild-type group (8.3 ± 4.1 vs. 5.7 ± 2.4, respectively; <i>P</i> = 0.03). Multivariate analysis indicated that SUV_max remained significantly associated with <i>KRAS</i> mutations (<i>P</i> = 0.04). <i>KRAS</i> status could be predicted with an accuracy of 71.4% when an SUV_max cutoff value of 6.0 was used. <b>Conclusion:</b>¹⁸F-FDG accumulation into metastatic CRC was associated with <i>KRAS</i> status. ¹⁸F-FDG PET/CT scans may be useful for predicting the <i>KRAS</i> status of metastatic CRC and help in determining the therapeutic strategies against metastatic CRC.