What you carry at this position in your DNA and what research says about it.
Lung Cancer Risk: 8/10 evidence, 15 publications.
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Sample genotype (not yours): C/C
Typical Lung Cancer Risk
Carrying two copies of the common C allele is associated with typical telomere length and a lower risk of several cancers. This genotype represents the protective baseline in the general population.
What this genotype means: Typical telomere length; Lower risk of lung and thyroid cancers; Lower risk of uterine fibroids.
Sample genotype (not yours): A/A
Higher Lung Cancer Risk
Carrying two copies of the A allele is associated with the longest telomeres and the highest risk of lung and thyroid cancers. This genotype also correlates with elevated red blood cell counts.
What this genotype means: Longer telomeres; Increased risk of lung and thyroid cancers; Higher red blood cell count.
Sample genotype (not yours): C/A
Moderately Increased Lung Cancer Risk
Carrying one copy of the A allele is associated with longer telomeres and a moderately increased risk of certain cancers. This genotype also correlates with slightly higher red blood cell counts.
What this genotype means: Slightly longer telomeres; Moderately increased risk of lung and thyroid cancers; Slightly higher red blood cell count.
Gene function and biological role
Gene Function: The TERT gene encodes the catalytic subunit of telomerase reverse transcriptase, an enzyme essential for maintaining telomere length at the ends of chromosomes. Telomeres act as protective caps that shorten with each cell division, serving as an internal clock for cellular aging. When telomerase is highly active, it rebuilds these caps, extending cellular lifespan and allowing cells to divide indefinitely [1]. While this cellular longevity is vital for stem cells, it can also enable pre-cancerous cells to evade normal cell death and accumulate harmful mutations [2]. Consequently, genetic variation in TERT represents a delicate biological trade-off between cellular aging and cancer susceptibility [3].
Variant Impact: The rs7726159 variant is an intronic change in the TERT gene that influences telomerase expression levels. The minor A allele is associated with increased TERT transcription and longer telomeres, which promotes cellular survival but increases cancer susceptibility [2]. Conversely, the major C allele is linked to shorter telomeres, which limits cellular lifespan and acts as a natural defense against tumor growth [2]. This variant is widely studied for its pleiotropic effects on cancer risk and blood cell traits across diverse populations [2].
Key Insight: Longer telomeres are generally associated with cellular youth, but at this genetic locus, the allele that lengthens telomeres actually increases the risk of several cancers by allowing abnormal cells to survive longer.
Location: TERT. Chromosome 5 · 5p15.33 · 1.3 Mb
Estimated prevalence by population
Global 50.1%; European 43.8%; African 65.5%; East Asian 37.6%; South Asian 34.5%; Americas 51.6%; Ashkenazi 39.3%; Finnish 47.3%; Middle Eastern 27.8%; Amish 46.1%.
Estimated CC genotype frequency.
Global 40.7%; European 44.8%; African 30.9%; East Asian 47.4%; South Asian 48.5%; Americas 40.5%; Ashkenazi 46.8%; Finnish 43.0%; Middle Eastern 49.9%; Amish 43.6%.
Estimated CA genotype frequency.
Global 9.2%; European 11.5%; African 3.6%; East Asian 15.0%; South Asian 17.0%; Americas 7.9%; Ashkenazi 13.9%; Finnish 9.8%; Middle Eastern 22.4%; Amish 10.3%.
Estimated AA genotype frequency.
Showing effects for C/C genotype
Cancer & Oncology
Lung Cancer
Lung Cancer. Evidence: 8/10. Source: PMID 37846649. Typical Risk.
Thyroid & Endocrine Cancers
Thyroid Cancer. Evidence: 4/10. Source: PMID 33527407. Typical Risk.
Endocrine & Reproductive
Female Reproductive Health & Fertility
Uterine Fibroids. Evidence: 6/10. Source: PMID 40050615. Typical Risk.
Cardiovascular & Metabolic
Blood Cell & Iron Traits
Red Blood Cell Count. Evidence: 9/10. Source: PMID 34594039. Typical.
Showing effects for A/A genotype
Lung Cancer. Evidence: 8/10. Source: PMID 37846649. ~1.4x Increased Risk.
Thyroid Cancer. Evidence: 4/10. Source: PMID 33527407. ~1.17x Increased Risk.
Uterine Fibroids. Evidence: 6/10. Source: PMID 40050615. Increased Risk.
Red Blood Cell Count. Evidence: 9/10. Source: PMID 34594039. Higher.
Showing effects for C/A genotype
Red Blood Cell Count. Evidence: 9/10. Source: PMID 34594039. Slightly Higher.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Carrying two copies of the C allele is associated with typical telomere length and a lower risk of developing lung cancer [1] and differentiated thyroid carcinoma [2]. Because telomeres are shorter in individuals with this genotype, cells have a more limited lifespan, which acts as a natural defense mechanism against uncontrolled tumor growth [3]. This genotype is also associated with a lower risk of uterine fibroids [4]. ClinVar assessments confirm that this variant does not cause rare telomere-shortening diseases like dyskeratosis congenita or idiopathic pulmonary fibrosis. Overall, this genotype represents a protective baseline against several common cancers.
Typical telomere length; Lower risk of lung and thyroid cancers; Lower risk of uterine fibroids.
Sample genotype: AA (Homozygous)
Carrying two copies of the A allele is associated with the highest level of TERT expression and the longest telomeres among the genotypes. While long telomeres are often associated with cellular youth, they also significantly increase the risk of lung cancer [1] and differentiated thyroid carcinoma [2]. The increased telomerase activity helps cancer cells evade the normal aging process and continue dividing [3]. This genotype is also linked to the highest risk of uterine fibroids [4]. Furthermore, individuals with this genotype tend to have higher red blood cell counts and hematocrit levels [5]. Despite the increased cancer risk, ClinVar classifies this variant as benign for rare telomere-shortening diseases like dyskeratosis congenita.
Longer telomeres; Increased risk of lung and thyroid cancers; Higher red blood cell count.
Sample genotype: CA (Heterozygous)
Carrying one copy of the A allele is associated with longer telomeres, which can promote cellular longevity but also increases the risk of cancer. Studies have linked this genotype to a moderately increased risk of lung cancer [1] and differentiated thyroid carcinoma [2]. The increased expression of TERT allows cells to divide more times, potentially giving pre-cancerous cells the opportunity to accumulate mutations [3]. This genotype is also associated with an increased risk of uterine fibroids [4]. Additionally, carriers may have slightly higher red blood cell counts and hematocrit levels [5]. While the risk is elevated, it is only one of many factors influencing cancer development.
Slightly longer telomeres; Moderately increased risk of lung and thyroid cancers; Slightly higher red blood cell count.
Variants with shared genetic architecture
rs2242652 · TERT Gene · Chr 5 · Cancer Risk Trade-offs
rs2735940 · TERT Gene · Chr 5 · Colorectal Cancer Risk
rs2853677 · TERT Gene · Chr 5 · Cancer Susceptibility
A cross-population atlas of genetic associations for 220 human phenotypes.
Content updated August 2026.
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