Patterns of KRAS, NRAS, and BRAF mutations in colorectal cancer in Chile: a 3-year real-world evidence [2019–2021]—a brief report

Introduction

Chile is experiencing a sustained and predictable increase in the incidence of colorectal cancer (CRC), primarily driven by rapid population aging and the absence of a fully implemented nationwide screening program within the national health system (1). Demographic projections based on the most recent national census, together with current estimates of the CRC burden, indicate that in the absence of organized early detection strategies, both CRC incidence and mortality will continue to rise steadily over the next decade, surpassing 8,700 new cases and 4,000 deaths annually by 2035 (2).

In contrast, the implementation of an organized, population-based early detection strategy, such as fecal immunochemical testing with colonoscopic follow-up, is expected to initially increase case detection rates, followed by a progressive and substantial reduction in CRC mortality (2).

In parallel with these population-level considerations, the molecular characterization of CRC has become increasingly relevant for therapeutic decision-making. International evidence consistently demonstrates that organized CRC screening programs are among the most effective interventions for reducing disease-specific mortality at the population level (3,4). These data are particularly relevant for Chile, where CRC mortality remains high despite advances in systemic therapies and surgical management (5). Our real-world evidence (RWE) registry of Chilean patients with CRC, collected between 2019 and 2021, includes a systematic assessment of KRAS, NRAS, and BRAF mutations, allowing us to quantify their prevalence and evaluate sex-specific differences in mutation frequency within this national cohort. However, while precision oncology enhances individualized care, it cannot offset the population-level consequences of late-stage diagnosis. Together, these considerations underscore that the future burden of CRC in Chile is not inevitable but modifiable, and that timely investment in organized screening, equitable access, and molecularly informed care represents one of the most impactful strategies to alter the current trajectory of the disease (6-8).

Methods

Study design and setting

Patients

A total of 999 patients with CRC were included in this study, comprising cases collected between 2019 and 2021 across participating institutions in Chile. These parameters were calculated separately for each year using the official clinical sex coding (1= male, 2= female). Comparing women vs. men was estimated using Fisher’s exact test for KRAS, NRAS, and BRAF mutations. Two-sided P values are reported. Cases not assignable were excluded from sex-stratified analyses (Table S1).

Inclusion and exclusion criteria

Patients were included if they had a confirmed diagnosis of CRC, available molecular testing for KRAS, NRAS, or BRAF, adequate tumor sample quality, and basic demographic data, including sex. The exclusion criteria comprised poor-quality or insufficient tumor material, inconclusive molecular results, duplicate records (only the first valid result retained), and missing essential clinical or demographic information. No restrictions were applied regarding disease stage (I–IV) or tumor status (primary, recurrent, or metastatic), reflecting the heterogeneity of real-world clinical practices. The cohort represented a consecutive testing population, minimizing selection bias.

Mutations in KRAS, NRAS, and BRAF genes

This type of mutations can be accurately identified using allele-specific quantitative polymerase chain reaction (qPCR)-based assays. These assays are extensively utilized in routine clinical practice because of their rapid turnaround time, minimal DNA input requirements, and compatibility with formalin-fixed, paraffin-embedded (FFPE) samples. However, these assays are restricted to predefined hotspot mutations and do not encompass the comprehensive range of genomic alterations that next-generation sequencing (NGS) can detect.

Odds ratios (ORs)

Confidence intervals (CIs) for ORs were derived using a parametric bootstrap approach based on binomial resampling within each sex stratum (10,000 iterations), applying a 0.5 continuity correction to avoid zero-cell instability. Two-sided P values were computed using Fisher’s exact test. KRAS, NRAS, and BRAF results were dichotomized as positive vs. negative based on the reported test result. Year-specific ORs comparing females vs. males were computed using Fisher’s exact test. For the combined analysis of KRAS, a multivariable logistic regression model was fitted, including year (continuous, mean-centered) and sex as covariates. To obtain robust uncertainty estimates for the adjusted sex effect, 95% CIs were computed using non-parametric bootstrap resampling (resampling patients with replacement; percentile method). Due to sparse event counts, reliable bootstrap CIs could not be estimated for NRAS and BRAF at the yearly level; therefore, these were presented descriptively as point estimates.

Ethical consideration

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This was a retrospective study including patients from multiple medical institutions in Chile. Due to the retrospective nature of the study and the use of previously collected, de-identified data, the requirement for individual informed consent was waived. All participating institutions were informed of the study and provided institutional authorizations. In accordance with local regulations in Chile, formal ethics committee approval was not required because of the retrospective design of the study.

Results

A total of 999 unique CRC patients were included in this real-world cohort between 2019 and 2021. The annual distribution showed a decrease in testing volume over time, with 524 patients in 2019, 290 in 2020, and 185 in 2021. The cohort included both male and female patients across all clinical stages, reflecting routine molecular testing practices. The overall distribution of oncogenic alterations in the cohort revealed that KRAS mutations were the most frequent across all years. In 2019, KRAS accounted for 73.2% of all detected alterations, representing approximately three-quarters of cases, whereas NRAS (12.9%) and BRAF (13.9%) mutations were less common, and each constituted a minority of cases. A similar pattern was observed in 2020, in which KRAS was the predominant gene (78.5%), compared with BRAF (11.0%) and NRAS (10.4%). In 2021, KRAS continued to dominate (71.8%), while BRAF represented 17.6% and NRAS 10.7% of cases. Overall, these results demonstrate a consistent predominance of KRAS mutations across the triennium, with relatively stable but lower frequencies of NRAS and BRAF alterations (Figure 1A).

Figure 1 Molecular landscape and sex-stratified mutation frequencies of KRAS, NRAS, and BRAF in Chilean CRC patients [2019–2021]. (A) Pie charts showing the relative frequency of KRAS (red), NRAS (yellow), and BRAF (green) mutations for each year. KRAS represents the predominant mutation across all years, accounting for 73.2% in 2019, 78.5% in 2020, and 71.8% in 2021, whereas NRAS and BRAF are less frequent. Bar plots comparing mutation frequencies between males (blue) and females (orange) for each gene in (B) year 2019, (C) year 2020, and (D) year 2021. In all years, KRAS mutations showed a higher frequency in females than in males, whereas NRAS and BRAF displayed variable distributions between sexes. Statistical comparisons were performed using the χ² or Fisher’s exact test as appropriate, and no statistically significant differences were observed (P=ns). Values are expressed as percentages within each group. CRC, colorectal cancer; ns, no significant.

Representation of sex-stratified mutation frequencies for KRAS, NRAS, and BRAF across 3 consecutive years, 2019–2021 (Figure 1B-1D). In 2019, KRAS mutations were more frequent in female patients compared with males (52.7% vs. 44.0%), while NRAS and BRAF mutations occurred at low frequencies with no statistically significant sex-related differences (Figure 1B). A similar pattern was observed in 2020, with a higher proportion of KRAS-mutated tumors in females (44.3% vs. 35.4%), and persistently low frequencies of NRAS and BRAF alterations in both sexes (Figure 1C). In 2021, KRAS mutation frequencies were comparable between females and males (40.7% vs. 39.4%), indicating attenuation of the sex-associated difference observed in earlier years. NRAS mutations remained rare in both sexes, and BRAF mutations showed a modest numerical increase in females, although this difference was not statistically significant (Figure 1D).

Overall, these findings indicate that KRAS is the dominant molecular alteration in this cohort, with a transient female predominance in KRAS mutation frequency in 2019–2020 that was not maintained in 2021. In contrast, NRAS and BRAF mutations were infrequent and did not demonstrate consistent sex-specific patterns over time.

Sex-associated differences in mutation prevalence were further evaluated using OR analyses comparing female and male patients across the 2019–2021 period. Year-specific estimates showed modest variability in the ORs for KRAS, NRAS, and BRAF, with wide CIs in individual years. In pooled analyses adjusted for year, KRAS mutations were significantly more frequent in females than in males (OR =1.35; 95% CI: 1.05–1.74; P=0.020), indicating a consistent female predominance across the study period. In contrast, no significant (ns) sex-related differences were observed for NRAS (pooled OR =0.76; 95% CI: 0.46–1.25) or BRAF (pooled OR =1.33; 95% CI: 0.85–2.10) mutations. Although BRAF showed an increased OR in females in 2021, this effect was not statistically significant in the pooled model, suggesting year-specific variability rather than a stable sex-associated pattern of the effect (Figure 2).

Figure 2 Sex-associated ORs of KRAS, NRAS, and BRAF mutations across 2019–2021. Forest plot displaying ORs with 95% CIs for the presence of gene mutations in female vs. male patients. Year-specific ORs (2019, 2020, and 2021) are shown for each gene, together with a pooled estimate adjusted for the year derived from logistic regression. Circles represent point estimates of the ORs, with horizontal lines indicating the 95% CIs; larger circles denote the pooled estimates. The dashed vertical line indicates a null effect (OR =1). Shaded backgrounds highlight the gene-specific panels (KRAS in red, NRAS in yellow, and BRAF in green). For KRAS, the pooled analysis demonstrated significantly higher ORs of mutation in females (OR =1.35; 95% CI: 1.05–1.74; P=0.02). In contrast, the pooled estimates for NRAS and BRAF did not show statistically significant sex-related differences. ns, no significant. Adj., adjusted; CI, confidence interval; OR, odds ratio.

Discussion

The most recent national census in Chile confirms a marked demographic shift toward older age groups, which disproportionately concentrate CRC risk and are expected to drive further increases in disease incidence and prevalence in the coming years (1,5). Despite advances in systemic therapies and surgical management, CRC mortality in Chile remains high, indicating that a substantial proportion of patients continue to be diagnosed at advanced stages of the disease (2). This unfavorable population-level trajectory reflects not only the biological progression of CRC but also persistent structural gaps in early detection, timely referral, and equitable access to specialized oncologic care (9).

In this context, molecular stratification, including the assessment of KRAS, NRAS, and BRAF mutation statuses, has become increasingly relevant for guiding therapeutic decision-making in advanced CRC (10). Nevertheless, while precision oncology improves individualized treatment selection, it cannot compensate for the population-level consequences of late-stage diagnoses (11). Our RWE registry provides valuable insight into the molecular landscape of CRC in Chile; however, these findings alone are insufficient to substantially modify outcomes in the absence of effective early detection strategies. Evidence from systematic reviews and program evaluations indicates that organized, population-based CRC screening programs are feasible in Latin American settings and can detect neoplasia at early, actionable stages, comparable to those observed in high-income countries (12). KRAS mutations are clinically relevant as predictive biomarkers of resistance to anti-EGFR therapies, making their distribution critical for treatment stratification. The observed sex-related differences in KRAS frequency may therefore influence personalized treatment decisions and overall outcomes. In contrast, NRAS and BRAF mutations did not show a consistent sex-associated pattern, suggesting that sex-related effects may preferentially impact KRAS-driven pathways. These findings support the inclusion of sex as an important variable in precision oncology for CRC (13). Furthermore, an early diagnosis is consistently associated with lower rates of emergency presentations and improved clinical outcomes in settings with established screening policies. This study had several limitations. Molecular testing was based on allele-specific qPCR targeting hotspot mutations in KRAS, NRAS, and BRAF, which provides limited genomic coverage compared with NGS and may underestimate non-hotspot mutations. In addition, testing was not uniformly performed across all genes in every patient, reflecting real-world practice in our country and introducing variability in the gene-specific denominators. Finally, MMR/MSI status was not consistently available, limiting the interpretation of BRAF-associated biology and comparisons with other cohorts.

Collectively, our results underscore the urgent need for integrated public health approaches that combine organized screening, age-targeted prevention, and molecularly informed treatment pathways to meaningfully alter the current trajectory of CRC in Chile and reduce its long-term clinical and socioeconomic burden. Implementing comprehensive screening policies supported by awareness campaigns, facilitated access, and sustained resource allocation is pivotal in achieving early diagnosis and reducing CRC mortality at the population level.

Real-world data from Chile show a high prevalence of KRAS mutations and lower but relevant frequencies of NRAS and BRAF alterations in CRC, with sex-specific patterns over time. Although molecular stratification refines therapeutic decision-making, it cannot compensate for the rising population burden driven by late diagnosis. Highlighting early detection as the cornerstone intervention to complement precision oncology strategies in Chile.

Acknowledgments

All participating institutions are listed in appendix available at https://cdn.amegroups.cn/static/public/jgo-2026-1-0110-1.docx.

Footnote

Peer Review File: Available at https://jgo.amegroups.com/article/view/10.21037/jgo-2026-1-0110/prf

Funding: This study was supported by FONDECYT (No. 1221499 to M.G.), Pfizer Investigator Sponsored Research (No. ISR CA209-8F3 to M.G.), and MERCK-Chile (to M.G.).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jgo.amegroups.com/article/view/10.21037/jgo-2026-1-0110/coif). M.G. reports funding from FONDECYT (No. 1221499). The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This was a retrospective study including patients from multiple medical institutions in Chile. Due to the retrospective nature of the study and the use of previously collected, de-identified data, the requirement for individual informed consent was waived. All participating institutions were informed of the study and provided institutional authorizations. In accordance with local regulations in Chile, formal ethics committee approval was not required because of the retrospective design of the study.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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