What you carry at this position in your DNA and what research says about it.
Colorectal Cancer Risk: 8/10 evidence, 33 publications.
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Sample genotype (not yours): C/C
Higher Colorectal Cancer Risk
Presence of the double-C genotype is associated with a moderately increased risk of developing colorectal cancer and precancerous colon polyps.
What this genotype means: Moderately increased risk of colorectal cancer; Higher likelihood of developing precancerous colon polyps; Reduced risk of esophageal cancer.
Sample genotype (not yours): A/A
Typical Colorectal Cancer Risk
Presence of the double-A genotype is associated with a typical risk of colorectal cancer and colon polyps.
What this genotype means: Typical baseline risk of colorectal cancer; Typical likelihood of developing colon polyps; Typical risk of esophageal cancer.
Sample genotype (not yours): C/A
Presence of a single C allele is associated with a moderately increased risk of developing colorectal cancer and precancerous colon polyps.
Gene function and biological role
Gene Function: The COLCA2 gene, also known as colorectal cancer associated 2, is located on chromosome 11q23.1 and plays a key role in the colon's immune microenvironment. It is co-regulated with its neighboring gene, COLCA1, and both are transcribed from opposite strands of DNA. COLCA2 protein is found in the cytoplasm of normal epithelial cells, tumor cells, and various immune cells in the colon. Research suggests that these genes are involved in local anti-tumor immune responses and inflammatory pathways. Altered expression of COLCA2 is strongly linked to susceptibility to colorectal tumors.
Variant Impact: Located within the chromosome 11q23.1 region, rs3802842 is an intron variant that acts as a regulatory marker influencing the expression levels of both COLCA1 and COLCA2 in the colon's lamina propria [1]. The risk-associated C allele is correlated with significantly lower levels of COLCA2 expression in colonic tissues [1]. This reduction in gene expression is thought to impair local immune defense mechanisms, making the colon more vulnerable to tumor development [1]. Additionally, this variant is associated with changes in local lymphocyte density within the intestinal lining [1].
Key Insight: The same genetic variant that increases the risk of colorectal cancer actually shows a protective effect against esophageal cancer. This highlights a complex evolutionary trade-off in digestive tract health.
Location: COLCA2. Chromosome 11 · 11q23.1 · 111.3 Mb
Estimated prevalence by population
Global 8.8%; European 8.1%; African 12.0%; East Asian 16.6%; South Asian 3.0%; Americas 5.0%; Ashkenazi 7.6%; Finnish 5.2%; Middle Eastern 3.8%; Amish 20.3%.
Estimated CC genotype frequency.
Global 40.8%; European 40.7%; African 45.3%; East Asian 48.3%; South Asian 28.6%; Americas 34.6%; Ashkenazi 39.9%; Finnish 35.2%; Middle Eastern 31.3%; Amish 49.5%.
Estimated CA genotype frequency.
Global 50.4%; European 51.3%; African 42.8%; East Asian 35.1%; South Asian 68.4%; Americas 60.4%; Ashkenazi 52.5%; Finnish 59.7%; Middle Eastern 65.0%; Amish 30.2%.
Estimated AA genotype frequency.
Showing effects for C/C genotype
Cancer & Oncology
Colorectal Cancer
Colorectal Cancer. Evidence: 8/10. Source: PMID 18372901. ~1.17x Increased Risk.
Colorectal Adenoma. Evidence: 8/10. Source: PMID 24801760. Increased Risk.
Gastrointestinal Cancers
Esophageal Cancer. Evidence: 3/10. Source: PMID 26078566. ~45% Reduced Risk.
Showing effects for A/A genotype
Colorectal Cancer. Evidence: 8/10. Source: PMID 18372901. Typical Risk.
Colorectal Adenoma. Evidence: 8/10. Source: PMID 24801760. Typical Risk.
Esophageal Cancer. Evidence: 3/10. Source: PMID 26078566. Typical Risk.
Showing effects for C/A genotype
Colorectal Cancer. Evidence: 8/10. Source: PMID 18372901. 1.17x Increased Risk.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Large-scale genome-wide association studies have consistently linked the C allele of this variant to an elevated risk of colorectal cancer [1]. Individuals with the C/C genotype have a moderately higher risk, estimated at over 1.17 times the typical population rate [2]. This genetic variant acts as a regulatory marker, with the C allele correlating with lower expression of the protective COLCA2 gene in the colon [3]. Lower expression of this gene is associated with reduced lymphocyte density and altered immune defense in the intestinal lining [3]. This genotype is also associated with a higher likelihood of developing conventional colorectal adenomas, which are precursor polyps [4]. Interestingly, research in Asian populations has found that the C/C genotype is associated with a significantly reduced risk of esophageal cancer [2]. This suggests a complex, tissue-specific role for this genetic locus across different parts of the digestive tract [2].
Moderately increased risk of colorectal cancer; Higher likelihood of developing precancerous colon polyps; Reduced risk of esophageal cancer.
Sample genotype: AA (Homozygous)
Two copies of the A allele are associated with a typical, baseline risk of developing colorectal cancer [1]. Multiple genome-wide association studies have confirmed that this genotype does not carry the elevated risk associated with the C allele [2]. At the molecular level, the A/A genotype is associated with higher, normal expression of the COLCA2 gene in the colon [3]. Normal expression of this gene helps maintain healthy lymphocyte density and robust immune surveillance within the intestinal lining [3]. Consequently, individuals with this genotype have a lower likelihood of developing conventional colorectal adenomas compared to C allele carriers [4]. However, this genotype does not confer the protective effect against esophageal cancer seen in carriers of the C allele [5]. Overall, this genetic profile represents the standard baseline for digestive tract health, and standard screening guidelines remain the most appropriate approach [1].
Typical baseline risk of colorectal cancer; Typical likelihood of developing colon polyps; Typical risk of esophageal cancer.
Sample genotype: CA (Heterozygous)
A single copy of the C allele is associated with a moderately increased risk of colorectal cancer, similar to the double-copy profile [1]. Studies indicate that carriers of this genotype have approximately a 1.17-fold increased risk of developing colorectal tumors [2]. The C allele functions as a regulatory variant that reduces the expression of the COLCA2 gene in the colon's mucosal lining [3]. This reduction in gene expression is linked to lower levels of local immune cells, potentially compromising the body's ability to clear early-stage abnormal cells [3]. Additionally, this genotype is associated with a higher risk of developing conventional colorectal adenomas, which are the precursor polyps that can progress to cancer [4]. Conversely, this same genotype has been shown to offer a protective effect against esophageal cancer, particularly in Chinese populations [2]. This dual effect highlights how a single genetic variant can have opposing impacts on different cancers within the digestive system [2].
Variants with shared genetic architecture
rs10505477 · CASC8 Gene · Chr 8 · Cancer Susceptibility Risk
rs16892766 · EIF3H Gene · Chr 8 · Colorectal Cancer Risk
rs2423279 · HAO1 Gene · Chr 20 · Colorectal Cancer Risk
Meta-analysis of new genome-wide association studies of colorectal cancer risk.
Content updated August 2026.
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