What you carry at this position in your DNA and what research says about it.
Breast Cancer Risk: 8/10 evidence, 51 publications.
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Sample genotype (not yours): T/T
Typical Breast Cancer Risk
Baseline breast cancer risk is typical for this genetic profile. It is also associated with slightly higher mammographic breast density.
What this genotype means: Typical baseline breast cancer risk; Slightly higher mammographic breast density.
Sample genotype (not yours): C/C
Elevated Breast Cancer Risk
An elevated risk of breast cancer is linked to this two-copy profile. It is also associated with lower mammographic breast density.
What this genotype means: Elevated breast cancer risk; Lower mammographic breast density.
Sample genotype (not yours): T/C
Slightly Elevated Breast Cancer Risk
A modest increase in breast cancer susceptibility is associated with this single-copy profile. It is also linked to slightly lower mammographic breast density.
What this genotype means: Modestly elevated breast cancer risk; Slightly lower mammographic breast density.
Gene function and biological role
Gene Function: The LSP1 gene encodes lymphocyte-specific protein 1, which is primarily expressed in white blood cells and endothelial cells. This protein plays an important role in the recruitment and migration of leukocytes during inflammatory responses [1]. It acts as an F-actin binding protein, helping to regulate the cytoskeleton and cell movement [1]. Beyond its role in immunology, genetic variations in LSP1 have been widely implicated in breast cancer susceptibility [2]. Studies suggest that LSP1 may influence tumor biology or the microenvironment surrounding breast tissue [2].
Variant Impact: Located within an intron of the LSP1 gene, rs3817198 is a non-coding genetic change. Because it does not directly alter the protein sequence, it is thought to influence how the gene is expressed or regulated [1]. This specific genetic marker is one of the most well-replicated low-penetrance susceptibility loci for breast cancer [2]. Interestingly, the risk-increasing allele is also associated with variations in mammographic breast density [3]. This dual association highlights the variant's complex role in breast tissue biology [3].
Key Insight: The C allele increases breast cancer risk but is actually associated with lower mammographic breast density, showing that genetic risk and physical breast density can be driven by opposite biological signals.
Location: LSP1. Chromosome 11 · 11p15.5 · 1.9 Mb
Estimated prevalence by population
Global 55.9%; European 46.6%; African 70.3%; East Asian 78.9%; South Asian 39.6%; Americas 59.4%; Ashkenazi 33.7%; Finnish 58.6%; Middle Eastern 45.4%; Amish 54.7%.
Estimated TT genotype frequency.
Global 36.9%; European 43.3%; African 27.1%; East Asian 19.8%; South Asian 46.7%; Americas 35.3%; Ashkenazi 48.7%; Finnish 35.9%; Middle Eastern 44.0%; Amish 38.5%.
Estimated TC genotype frequency.
Global 7.2%; European 10.1%; African 2.6%; East Asian 1.2%; South Asian 13.7%; Americas 5.2%; Ashkenazi 17.6%; Finnish 5.5%; Middle Eastern 10.7%; Amish 6.8%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Cancer & Oncology
Breast Cancer
Breast Cancer. Evidence: 8/10. Source: PMID 17529967. Typical Risk.
Mammographic Density. Evidence: 5/10. Source: PMID 22454379. Slightly Higher.
Showing effects for C/C genotype
Breast Cancer. Evidence: 8/10. Source: PMID 17529967. ~1.12x Risk.
Mammographic Density. Evidence: 5/10. Source: PMID 22454379. Slightly Lower.
Showing effects for T/C genotype
Breast Cancer. Evidence: 8/10. Source: PMID 17529967. ~1.06x Risk.
Mammographic Density. Evidence: 5/10. Source: PMID 22454379. Typical.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Two copies of the T allele represent the most common genetic profile globally. Large-scale genome-wide association studies have established that this genotype does not carry the elevated breast cancer risk associated with the C allele [1]. However, research shows that the T allele is linked to slightly higher mammographic breast density [2]. Mammographic density refers to the proportion of fibroglandular tissue visible on a mammogram, which is itself a known marker for breast health [2]. Despite having higher breast density, individuals with this genotype maintain a typical baseline risk for developing breast cancer [1]. This highlights how genetic markers can influence physical traits and disease risks through separate pathways. Understanding these baseline patterns helps researchers build more accurate risk prediction models [3]. Most clinical risk assessments treat this common genotype as the standard comparison group [3].
Typical baseline breast cancer risk; Slightly higher mammographic breast density.
Sample genotype: CC (Homozygous)
Two copies of the C allele are associated with the highest relative risk of breast cancer at this locus [1]. Meta-analyses involving over 70,000 participants confirm that the C allele increases breast cancer risk in a dose-dependent manner [2]. For individuals of European ancestry, this genotype represents an approximate ten to twelve percent increase in relative risk [3]. Conversely, some preliminary evidence suggests this variant's effect may differ or even be protective in women of African ancestry [4]. Despite the increased cancer risk, this genotype is associated with lower mammographic breast density, highlighting a complex biological mechanism [5]. This paradox suggests that the variant's impact on cancer risk does not rely on increasing dense breast tissue [5]. Instead, it may alter immune cell behavior or localized inflammation within the breast microenvironment [1]. While the relative risk is elevated, the absolute increase in lifetime risk remains modest for most individuals [6].
Elevated breast cancer risk; Lower mammographic breast density.
Sample genotype: TC (Heterozygous)
One copy of the C allele is associated with a modest increase in breast cancer susceptibility [1]. Large genetic analyses, including studies of tens of thousands of cases, have consistently identified this variant as a low-penetrance risk factor [2]. The C allele is estimated to increase the relative risk of breast cancer by approximately six percent per copy [1]. Interestingly, while the C allele increases cancer risk, it is actually associated with slightly lower mammographic breast density [3]. This suggests that the genetic pathway by which this variant influences cancer risk may operate independently of visible breast tissue density [3]. Researchers continue to study how these non-coding variants alter gene expression in breast tissue [1]. For most people, this single-copy change represents only a very small shift in overall lifetime risk [4]. It is typically evaluated alongside other genetic and lifestyle factors to paint a complete picture [4].
Modestly elevated breast cancer risk; Slightly lower mammographic breast density.
Variants with shared genetic architecture
rs981782 · HCN1 Gene · Chr 5 · Breast Cancer Risk
rs11820646 · LINC01395 Gene · Chr 11 · Breast Cancer Risk
rs1219648 · FGFR2 Gene · Chr 10 · Breast Cancer Risk
Genome-wide association study identifies novel breast cancer susceptibility loci.
Performance of common genetic variants in breast-cancer risk models.
Evaluation of 19 susceptibility loci of breast cancer in women of African ancestry.
Content updated August 2026.
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