Clinicopathological Profiles Associated with Discordant RAS Mutational Status between Liquid and Tissue Biopsies in a Real-World Cohort of Metastatic Colorectal Cancer

Abstract

We aimed to identify common mCRC profiles associated with a discordant mutational status of RAS between the standard of care (SoC) tumour tissue tests and ctDNA tests to understand ctDNA detection and improve treatment responses. This was a multicentre, retrospective and prospective study. A total of 366 Spanish mCRC patients were independently recruited. BEAMing ddPCR technology was employed to detect ctDNA RAS mutations, and logistic regression analyses were performed to investigate clinicopathological factors associated with discordance. The highest concordance ratios were observed in profiles with multiple metastatic sites when the liver was present (89.7%; 95% CI 84.8-93.2), profiles with synchronous disease without primary tumour resection (90.2%; 95% CI 83.6-94.3) and profiles with mCRC originating in the left colon (91.3%; 95% CI 85.0-95.0). Metachronous disease originating in the right colon (OR = 6.1; 95% CI 1.7-26.5; p-value = 0.006) or rectum (OR = 5.0; 95% CI 1.5-17.8; p-value = 0.009) showed the highest probability of discrepancies. Primary tumour resection and a higher frequency of single metastases in the peritoneum or lungs in these patients were associated with reduced plasmatic mutation allele fractions (MAFs) and an increased probability of showing false-negative genotypes. Additional testing of patients with mCRC originating in the right colon or rectum with a single non-mutated ctDNA test is advised before the choice of therapy.

Keywords: RAS; anti-EGFR therapy; colorectal cancer; ctDNA; liquid biopsy; mCRC; metastatic colorectal cancer.

Figure 1

Impact of the mCRC clinicopathological characteristics on the detection of plasmatic RAS mutations. (a) Impact of the metastatic site on the plasmatic RAS MAFs. Dark blue dots (column 1) represent ctDNA RAS MAFs of patients with at least one liver metastasis. Light blue dots (column 2) represent ctDNA RAS MAFs of patients with at least one metastatic site at other anatomical locations than the liver. Lines represent the median and the 25–75% IQR. (b) Impact of surgical treatment and palliative/life-extending systemic chemotherapy on the ctDNA RAS MAFs. Plasmatic RAS mutations were detected in 113 patients with synchronous metastases and chemotherapy-naive and in 43 patients with metachronous metastases who had been at least previously treated by tumour surgery. Dark orange dots (column 1) represent ctDNA RAS MAFs of 69 patients with newly diagnosed synchronous mCRC who had not received surgical treatment. Light orange dots (column 2) represent ctDNA RAS MAFs of patients with synchronous metastases treated with resection of the primary tumour (4 had also been subjected to the removal of metastatic tissue). Yellow dots represent (column 3) ctDNA RAS MAFs of 43 patients with metachronous metastases; 34 had only been treated with resection of the primary tumour and 9 had been treated with resection of primary and metastatic tumour tissue. Adjuvant systemic chemotherapy had been administered to 24 of the cases before plasma collection. Lines represent the median and the 25–75% IQR. (c) Plasmatic RAS MAFs in patients with synchronous mCRC and different origins of the primary tumour who were not subjected to previous tumour surgery or systemic chemotherapy. Blue, green and red dots represent ctDNA RAS MAFs of patients with mCRC that originated in the left colon, rectum and right colon, respectively. Lines represent the median and the 25–75% IQR. (d) Plasmatic RAS MAFs from patients with primary tumours in different locations and treated with surgical resection. Blue, green and red dots represent ctDNA RAS MAFs of patients with mCRC that originated in the left colon, rectum and right colon, respectively. Colour gradients were used to show the decrease in the RAS MAFs in the mCRC subpopulations treated with resection of the primary tumour. Lines represent the median and the 25–75% IQR. (e) Correlation of primary tumour location with the metastatic pattern of mCRC. Plots showed the number of metastatic sites (e) and the anatomical location of the metastases (f) in 242 patients with synchronous tumours. All patients were naive to surgery or chemotherapy. The frequency of only one single site of metastasis was higher in patients with primary tumours located in the right colon. The liver was the predominant site of metastasis in mCRC with left colon origin, whereas lung metastases were more frequent in mCRC originating at the rectum. Peritoneal metastases and metastases to other sites were frequent in right-sided mCRC. Non-parametric Mann–Whitney U and Kruskal–Wallis tests were used to calculate p-values when two or more groups were compared.