What you carry at this position in your DNA and what research says about it.
Environmental Cancer Risk: 5/10 evidence, 54 publications.
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Sample genotype (not yours): T/T
Typical Environmental Cancer Risk
Two copies of the reference allele encode the standard-activity enzyme. This results in typical baseline risks for toxin-related cancers.
What this genotype means: Typical baseline risk of lung and breast cancers; Standard clearance of environmental toxins; Typical sensitivity to taxane-based chemotherapies.
Sample genotype (not yours): C/C
Elevated Environmental Cancer Risk
Two copies of the hyperactive variant allele significantly accelerate the activation of environmental toxins. This is associated with higher risks for several cancers.
What this genotype means: Elevated risk of lung cancer, especially with tobacco exposure; Increased susceptibility to breast and laryngeal cancers; Enhanced response to certain chemotherapies alongside higher toxicity risks.
Sample genotype (not yours): T/C
Slightly Elevated Environmental Cancer Risk
One copy of the hyperactive variant allele slightly increases the rate of toxin activation. This is linked to a modest increase in environmental cancer risks.
What this genotype means: Slightly increased susceptibility to smoke-related lung cancer; Modestly elevated risk of breast and laryngeal cancers; Potential for enhanced docetaxel response but higher side-effect risk.
Gene function and biological role
Gene Function: The CYP1A1 gene encodes cytochrome P450 1A1, a key phase I enzyme responsible for metabolizing polycyclic aromatic hydrocarbons (PAHs) found in tobacco smoke, charred meats, and industrial air pollution [1]. It also plays a critical role in the metabolic breakdown of estrogens [2]. While designed to detoxify foreign substances, this enzyme can sometimes bioactivate inert environmental chemicals into highly reactive, mutagenic intermediates [1]. These reactive compounds can bind directly to DNA, forming harmful adducts that may initiate cancer if not properly cleared [1]. Consequently, variations in this gene significantly influence how the body processes environmental toxins and hormones.
Variant Impact: The rs1048943 variant, also known as Ile462Val or CYP1A1*2C, is a missense mutation in exon 7 that replaces the amino acid isoleucine with valine [1]. This structural change occurs near the heme-binding domain, resulting in an enzyme with approximately twofold higher catalytic activity and increased inducibility [3]. Because the altered enzyme processes environmental carcinogens and estrogens at an accelerated rate, it leads to a higher accumulation of reactive DNA-damaging intermediates [1] [3]. This heightened metabolic activity is linked to an elevated susceptibility to several cancers, particularly when combined with tobacco exposure [4]. It also alters the processing of certain chemotherapy drugs, affecting both treatment efficacy and side-effect profiles [5].
Key Insight: The valine-encoding variant increases enzyme activity rather than disabling it, meaning carriers actually produce more DNA-damaging chemical intermediates when exposed to smoke or pollution.
Location: CYP1A1. Chromosome 15 · 15q24.1 · 74.7 Mb
Estimated prevalence by population
Global 88.3%; European 93.0%; African 97.1%; East Asian 57.4%; South Asian 77.7%; Americas 55.9%; Ashkenazi 93.8%; Finnish 88.4%; Middle Eastern 87.5%; Amish 89.5%.
Estimated TT genotype frequency.
Global 10.7%; European 6.8%; African 2.8%; East Asian 36.7%; South Asian 20.9%; Americas 37.7%; Ashkenazi 6.1%; Finnish 11.2%; Middle Eastern 12.1%; Amish 10.2%.
Estimated TC genotype frequency.
Global 1.0%; European 0.1%; African < 0.1%; East Asian 5.9%; South Asian 1.4%; Americas 6.4%; Ashkenazi 0.1%; Finnish 0.4%; Middle Eastern 0.4%; Amish 0.3%.
Estimated CC genotype frequency.
Showing effects for T/T genotype
Cancer & Oncology
Lung Cancer
Lung Cancer. Evidence: 4/10. Source: PMID 23832578. Typical Risk.
Breast Cancer
Breast Cancer. Evidence: 4/10. Source: PMID 23000097. Typical Risk.
Head, Neck & Oral Cancers
Laryngeal Cancer. Evidence: 4/10. Source: PMID 32882964. Typical Risk.
Pharmacogenomics
Chemotherapy Response
Docetaxel Response. Evidence: 5/10. Source: PMID 22426923. Typical Response.
Sunitinib Toxicity. Evidence: 5/10. Source: PMID 19667267. Typical Risk.
Showing effects for C/C genotype
Lung Cancer. Evidence: 4/10. Source: PMID 23832578. Higher Risk.
Breast Cancer. Evidence: 4/10. Source: PMID 23000097. Higher Risk.
Laryngeal Cancer. Evidence: 4/10. Source: PMID 32882964. Higher Risk.
Docetaxel Response. Evidence: 5/10. Source: PMID 22426923. Stronger Response.
Sunitinib Toxicity. Evidence: 5/10. Source: PMID 19667267. Higher Toxicity Risk.
Showing effects for T/C genotype
Lung Cancer. Evidence: 4/10. Source: PMID 23832578. Slightly Higher Risk.
Breast Cancer. Evidence: 4/10. Source: PMID 23000097. Slightly Higher Risk.
Laryngeal Cancer. Evidence: 4/10. Source: PMID 32882964. Slightly Higher Risk.
What this genotype means for the people who carry it
Sample genotype: TT (Homozygous)
Standard metabolic processing of environmental pollutants and estrogens is maintained by this genotype [1]. Because the resulting enzyme does not exhibit hyperactive kinetics, there is no accelerated generation of reactive DNA-damaging intermediates from tobacco smoke or charred foods [2]. Studies consistently show typical baseline risks for lung, breast, and laryngeal cancers compared to carriers of the variant allele [3] [4]. In the context of chemotherapy, standard drug clearance rates are expected, meaning typical response and side-effect profiles for medications like docetaxel and sunitinib [5] [6]. Maintaining a healthy lifestyle free of tobacco smoke remains the most effective way to support natural detoxification pathways.
Typical baseline risk of lung and breast cancers; Standard clearance of environmental toxins; Typical sensitivity to taxane-based chemotherapies.
Sample genotype: CC (Homozygous)
Exclusive production of the hyperactive valine-containing enzyme characterizes this homozygous genotype [1]. This rapid enzymatic activity significantly accelerates the conversion of environmental toxins, such as polycyclic aromatic hydrocarbons, into highly reactive DNA-damaging compounds [2]. Multiple meta-analyses have linked this genotype to a significantly elevated risk of lung, breast, and laryngeal cancers, with the risk being most pronounced in smokers [3] [4]. In oncology settings, this genotype is associated with a highly favorable tumor response to docetaxel and capecitabine, though patients may experience more severe gastrointestinal toxicities [5]. There is also a marked increase in the risk of severe side effects, such as mucositis and low white blood cell counts, when taking the drug sunitinib [6]. Avoiding tobacco smoke and minimizing environmental toxin exposure are critical preventive strategies for individuals with this genetic profile.
Elevated risk of lung cancer, especially with tobacco exposure; Increased susceptibility to breast and laryngeal cancers; Enhanced response to certain chemotherapies alongside higher toxicity risks.
Sample genotype: TC (Heterozygous)
Co-expression of both the standard and hyperactive forms of the enzyme occurs with this heterozygous genotype [1]. The presence of the valine-encoding variant slightly accelerates the bioactivation of inhaled or ingested carcinogens into reactive, mutagenic compounds [2]. Research indicates a modest increase in susceptibility to lung, breast, and laryngeal cancers, particularly among individuals exposed to heavy tobacco smoke [3] [4]. On the clinical front, this genotype is associated with a higher likelihood of positive response to the chemotherapy drug docetaxel, though it may also elevate the risk of gastrointestinal side effects [5]. Additionally, there is a slightly increased risk of experiencing low white blood cell counts during sunitinib treatment [6]. Minimizing exposure to secondhand smoke, air pollution, and heavily charred meats is highly beneficial for managing these risks.
Slightly increased susceptibility to smoke-related lung cancer; Modestly elevated risk of breast and laryngeal cancers; Potential for enhanced docetaxel response but higher side-effect risk.
Variants with shared genetic architecture
rs2470893 · CYP1A1 Gene · Chr 15 · Caffeine and Kidney Health
rs2472297 · CYP1A1 Gene · Chr 15 · Caffeine and Kidney Health
rs4646421 · CYP1A1 Gene · Chr 15 · Toxin Metabolism and Cancer
Cytochrome P450 1A1 (CYP1A1) polymorphisms and breast cancer risk in Korean women.
Pharmacogenetic pathway analysis for determination of sunitinib-induced toxicity.
Content updated August 2026.
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