What you carry at this position in your DNA and what research says about it.
Breast Cancer Risk: 10/10 evidence, 59 publications.
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Sample genotype (not yours): A/A
Typical Breast Cancer Risk
Two copies of the protective A allele are associated with a typical baseline risk of developing breast cancer. This genotype avoids the slight risk elevation linked to the G variant.
What this genotype means: Typical baseline risk of breast cancer; No genetic elevation of 8q24-mediated oncogene expression.
Sample genotype (not yours): A/G
Slightly Increased Breast Cancer Risk
Possessing one copy of the G allele is linked to a slightly higher risk of developing breast cancer. This risk is modest and is often associated with more treatable, hormone-receptor-positive tumor subtypes.
What this genotype means: Slightly increased risk of breast cancer; Predisposition to hormone-receptor-positive tumor subtypes if cancer develops.
Sample genotype (not yours): G/G
Increased Breast Cancer Risk
Carrying two copies of the G allele is associated with an increased risk of developing breast cancer. If breast cancer does develop, it is more likely to be a hormone-receptor-positive, lower-grade subtype.
What this genotype means: Increased risk of breast cancer; Higher likelihood of developing lower-grade, hormone-responsive tumors if diagnosed.
Gene function and biological role
Gene Function: The CASC8 gene is located in the 8q24 chromosomal region, a well-known gene desert that contains multiple independent variants linked to cancer risk [1]. This region contains long-range enhancers that regulate the expression of MYC, a powerful oncogene that drives cell growth and division [2]. CASC8 itself encodes a long non-coding RNA that plays a regulatory role in cellular pathways [3]. Genetic variations in this gene have been consistently associated with susceptibility to various cancers, particularly breast, prostate, and colorectal cancers [4].
Variant Impact: The rs13281615 variant is an intronic single nucleotide polymorphism located within the CASC8 gene on chromosome 8 [5]. This genetic change alters the regulatory landscape of the 8q24 region, influencing the activity of nearby genes involved in cell proliferation [3]. The G allele of this variant is a well-documented risk factor that slightly increases the likelihood of developing breast cancer [6]. Interestingly, this variant shows a stronger association with estrogen receptor-positive and low-grade tumors compared to more aggressive subtypes [7].
Key Insight: While the G allele increases the risk of developing breast cancer, some studies suggest it is also associated with a slightly better overall survival rate post-diagnosis, likely because it predisposes to less aggressive, hormone-receptor-positive tumor subtypes.
Location: CASC8. Chromosome 8 · 8q24.21 · 127.3 Mb
Estimated prevalence by population
Global 31.8%; European 34.3%; African 31.3%; East Asian 23.8%; South Asian 23.8%; Americas 21.4%; Ashkenazi 31.4%; Finnish 42.9%; Middle Eastern 20.8%; Amish 18.5%.
Estimated AA genotype frequency.
Global 48.8%; European 48.5%; African 49.3%; East Asian 50.0%; South Asian 50.0%; Americas 49.7%; Ashkenazi 49.3%; Finnish 45.2%; Middle Eastern 49.6%; Amish 49.0%.
Estimated AG genotype frequency.
Global 19.4%; European 17.2%; African 19.4%; East Asian 26.2%; South Asian 26.2%; Americas 28.8%; Ashkenazi 19.3%; Finnish 11.9%; Middle Eastern 29.6%; Amish 32.5%.
Estimated GG genotype frequency.
Showing effects for A/A genotype
Cancer & Oncology
Breast Cancer
Breast Cancer. Evidence: 10/10. Source: PMID 17529967. Typical Risk.
ER-Negative Breast Cancer. Evidence: 10/10. Source: PMID 29058716. Typical Risk.
Cancer Prognosis & Treatment Outcome
Breast Cancer Prognosis. Evidence: 10/10. Source: PMID 21596841. Typical Prognosis.
Showing effects for A/G genotype
Breast Cancer. Evidence: 10/10. Source: PMID 17529967. Slightly Increased.
ER-Negative Breast Cancer. Evidence: 10/10. Source: PMID 29058716. Slightly Increased.
Breast Cancer Prognosis. Evidence: 10/10. Source: PMID 21596841. Slightly Favorable.
Showing effects for G/G genotype
Breast Cancer. Evidence: 10/10. Source: PMID 17529967. Increased Risk.
ER-Negative Breast Cancer. Evidence: 10/10. Source: PMID 29058716. Increased Risk.
Breast Cancer Prognosis. Evidence: 10/10. Source: PMID 21596841. Favorable Prognosis.
What this genotype means for the people who carry it
Sample genotype: AA (Homozygous)
The A/A genotype represents two copies of the common, protective allele at this chromosome 8q24 locus [1]. Large-scale genome-wide association studies have consistently shown that individuals with this genotype have the lowest risk of developing breast cancer compared to those carrying the G risk allele [2]. This protective effect applies to both estrogen receptor-positive and estrogen receptor-negative breast cancer subtypes [3]. The absence of the G allele means there is no genetic elevation in the expression of nearby oncogenes like MYC driven by this specific locus [4]. While this genotype is highly favorable, it does not make one immune to breast cancer, as environmental factors and other genetic loci also play significant roles.
Typical baseline risk of breast cancer; No genetic elevation of 8q24-mediated oncogene expression.
Sample genotype: AG (Heterozygous)
The A/G genotype represents one copy of the G risk allele at rs13281615, which is associated with a modest increase in breast cancer susceptibility [1]. This genetic variant lies in a regulatory region on chromosome 8q24 that can influence the activity of the MYC oncogene, which promotes cell growth [2]. Interestingly, the risk associated with this variant is more pronounced for estrogen receptor-positive and low-grade tumors, which generally have a more favorable prognosis and respond well to hormone therapies [3]. Some clinical studies have noted that breast cancer patients with this variant may experience slightly better survival outcomes, primarily because the tumors they develop tend to be less aggressive [4]. This slight risk elevation is just one of many factors influencing breast health. Maintaining routine clinical screenings and discussing personal risk factors with a healthcare provider remains the most effective approach to prevention.
Slightly increased risk of breast cancer; Predisposition to hormone-receptor-positive tumor subtypes if cancer develops.
Sample genotype: GG (Homozygous)
The G/G genotype at this locus is linked to the highest relative risk of breast cancer for this specific variant, with a modest increase in susceptibility compared to the typical genotype [1]. This variant is located within the CASC8 gene in the 8q24 region, which acts as a long-range enhancer regulating cell proliferation pathways [2]. The increased risk is particularly associated with estrogen receptor-positive and progesterone receptor-positive breast cancers [3]. Although the risk of developing cancer is elevated, research indicates that G-allele carriers who are diagnosed with breast cancer often have a slightly better prognosis [4]. This is because the resulting tumors are more likely to be low-grade and highly responsive to standard endocrine therapies [3]. Understanding this genetic predisposition can help personalize wellness strategies. It is important to focus on modifiable lifestyle factors and adhere to recommended breast cancer screening guidelines.
Increased risk of breast cancer; Higher likelihood of developing lower-grade, hormone-responsive tumors if diagnosed.
Variants with shared genetic architecture
rs10505477 · CASC8 Gene · Chr 8 · Cancer Susceptibility Risk
rs1447295 · CASC8 Gene · Chr 8 · Prostate Cancer Risk
rs6983267 · CASC8 Gene · Chr 8 · Cancer Risk
Multiple loci with different cancer specificities within the 8q24 gene desert.
Long-range enhancers on 8q24 regulate c-Myc.
Pooled analysis of genetic variation at chromosome 8q24 and colorectal neoplasia risk.
Genome-wide association study identifies novel breast cancer susceptibility loci.
Identification of ten variants associated with risk of estrogen-receptor-negative breast cancer.
Association analysis identifies 65 new breast cancer risk loci.
Content updated August 2026.
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