TOX3 rs3803660: What Your Genotype Means
The rs3803660 variant is a single nucleotide polymorphism located within the TOX3 gene region. Research has associated this specific genetic marker with a moderately increased risk of developing estrogen receptor-positive (ER+) breast cancer.
What each genotype means
Baseline breast cancer risk
This genotype represents the non-risk version of the variant associated with the TOX3 gene. Research indicates that individuals with this genotype do not carry the specific allele linked to a moderately increased risk of estrogen receptor-positive breast cancer. This result should be viewed as part of your overall genetic background rather than a standalone indicator of health.
This genotype is common in populations of European ancestry, occurring in approximately 55% of individuals.
Slightly increased risk profile
Carrying one copy of this variant is associated with a statistically modest increase in the risk of developing estrogen receptor-positive breast cancer. This association is based on population-level data and does not determine individual health outcomes. You should continue to follow standard breast cancer screening guidelines recommended by your healthcare provider.
This genotype is found in roughly 38% of individuals of European ancestry.
Elevated breast cancer risk
This genotype is associated with a moderately increased risk of developing estrogen receptor-positive breast cancer compared to those without the variant. While this genetic marker is a known factor in breast cancer susceptibility, it is only one of many influences on your health. Please discuss your family history and appropriate screening schedules with your physician.
This genotype is present in approximately 7% of individuals of European ancestry.
Understanding the Variant
The variant rs3803660 is a single nucleotide polymorphism, or SNP, which is a variation at a single position in the DNA sequence. This specific SNP is located on chromosome 16 within the TOX3 gene locus. In genomics, SNPs like rs3803660 are often identified through genome-wide association studies (GWAS), which compare the DNA of individuals with a specific condition to those without it to find common genetic markers. While this variant is located in a region associated with breast cancer susceptibility, it is important to understand that it is a common variation found in the general population. Being a carrier of a specific allele at this site does not mean an individual will develop a disease; rather, it represents a small, incremental change in the statistical likelihood of a specific health outcome when viewed across large populations.
The Role of the TOX3 Gene
The TOX3 gene, which stands for TOX high mobility group box family member 3, encodes a protein that plays a role in cellular processes. Research indicates that TOX3 is expressed in mammary epithelial cells and is involved in regulating estrogen receptor target genes. Because estrogen receptor-positive (ER+) breast cancer relies on estrogen signaling for growth, the function of TOX3 in these cells is a subject of ongoing scientific interest. Studies have suggested that the protein may influence cell proliferation, migration, and survival. When the gene is overexpressed or its regulation is altered, it may contribute to the development or progression of certain tumor types. Understanding how variants near or within this gene influence its expression is a key area of research aimed at deciphering the complex genetic architecture of breast cancer.
Evidence and Associations
The association between the TOX3 locus and breast cancer is supported by multiple large-scale genetic studies. Specifically, variants in this region have been linked to an increased risk of estrogen receptor-positive breast cancer. However, the evidence strength for any single SNP, including rs3803660, is often categorized as limited or moderate in terms of individual predictive power. Genetic risk is polygenic, meaning it is influenced by the cumulative effect of many different variants across the entire genome, rather than a single "breast cancer gene." While the statistical association is reproducible in many studies, the actual increase in risk conferred by this single variant is relatively small. It is essential to view this information as a piece of a much larger puzzle that includes environmental factors, lifestyle, and other genetic markers.
Population Frequency
The frequency of genetic variants can vary significantly depending on an individual's ancestral background. For rs3803660, the minor allele frequency is approximately 0.26 in European populations. This means that a significant portion of the population carries at least one copy of this allele. Because this variant is relatively common, it is considered a low-penetrance susceptibility marker. This contrasts with rare, high-penetrance mutations in genes like BRCA1 or BRCA2, which carry a much higher risk of disease. Because the variant is common, it is not a rare "disease-causing" mutation but rather a common variation that contributes to the natural genetic diversity observed in humans. Researchers continue to study these frequencies across diverse global populations to better understand how genetic risk factors are distributed worldwide.
What This Information Means for You
If you have received information about your genotype for rs3803660, it is important to maintain perspective. This variant is a common genetic marker and is not a diagnostic tool for breast cancer. Having a specific genotype does not mean you will develop cancer, nor does the absence of the risk allele guarantee protection. Genetic testing for common variants like this is generally not used for clinical decision-making or individual risk assessment in a standard medical setting. If you have concerns about your personal or family history of breast cancer, the most effective step is to consult with a healthcare provider or a genetic counselor. They can evaluate your overall risk profile, including family history and other clinical factors, to provide personalized guidance on screening and preventative health measures.
How common is this variant?
The minor allele frequency for rs3803660 is approximately 0.26 in European ancestries, making it a common variant in that population.
Frequently asked questions
Does having the risk allele mean I will get breast cancer?
No. This variant is a common genetic marker associated with a small, statistical increase in risk. It is not a diagnostic test and does not determine whether or not you will develop the disease.
Should I get tested for this SNP?
Genetic testing for common, low-risk variants like rs3803660 is generally not recommended for clinical use. If you are concerned about your breast cancer risk, speak with a doctor about your family history and established screening guidelines.
Is this the same as a BRCA mutation?
No. BRCA1 and BRCA2 mutations are rare, high-penetrance variants that significantly increase cancer risk. The TOX3 variant is a common, low-penetrance marker with a much smaller effect on risk.
Can I change my risk if I have this genotype?
While you cannot change your genetics, you can manage your overall health through lifestyle choices and regular medical screenings. Always follow the advice of your healthcare provider regarding appropriate cancer screening schedules.
Sources & further reading
Educational information only, last refreshed 9/29/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Intronic susceptibility locus strongly associated with altered TOX3 enhancer activity and increased risk of estrogen receptor-positive breast cancer.
A common intergenic risk allele at the 16q12/TOX3 locus strongly associated with estrogen receptor-positive breast cancer susceptibility.
Variant in a non-coding regulatory element modulating FOXA1 binding and chromatin affinity, significantly influencing TOX3 expression and predisposition to breast cancer.