What you carry at this position in your DNA and what research says about it.
Prostate Cancer Risk: 6/10 evidence, 61 publications.
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Sample genotype (not yours): C/C
Higher Cancer Risk and Faster Drug Metabolism
Two copies of the CYP3A4*1B variant are linked to an increased risk of prostate and ovarian cancers. This genotype also causes rapid clearance of several medications, potentially reducing their effectiveness.
What this genotype means: Increased risk of prostate and ovarian cancers; Rapid clearance of tacrolimus, with lower blood levels; Reduced response to cyclophosphamide chemotherapy.
Sample genotype (not yours): C/T
Typical Cancer Risk with Faster Drug Metabolism
Possession of one copy of the CYP3A4*1B variant does not significantly raise cancer risk but still accelerates the clearance of certain medications.
What this genotype means: Accelerated clearance of tacrolimus; Poorer response to cyclophosphamide chemotherapy; Typical baseline cancer risk.
Sample genotype (not yours): T/T
Typical Cancer Risk and Normal Drug Metabolism
Two copies of the normal T allele are associated with typical baseline risks for prostate and ovarian cancers. This genotype also ensures standard metabolism rates for many common medications.
What this genotype means: Typical baseline risk for prostate and ovarian cancers; Standard clearance of tacrolimus with lower rejection risk; Expected response to atorvastatin and cyclophosphamide.
Gene function and biological role
Gene Function: The CYP3A4 gene encodes cytochrome P450 3A4, one of the most important drug-metabolizing enzymes in the human body. Located primarily in the liver and intestines, this enzyme is responsible for breaking down roughly half of all commonly prescribed clinical medications [1]. It also plays a vital physiological role in metabolizing endogenous steroid hormones, including estrogens and androgens [2]. Variations in this gene can dramatically alter how quickly a person clears specific medications, directly impacting drug efficacy and the risk of side effects [3].
Variant Impact: The rs2740574 variant is located in the promoter region of the CYP3A4 gene, where it alters the transcription rate of the enzyme. The C allele defines the well-studied CYP3A4*1B variant, which is associated with altered expression levels of the enzyme [2]. This genetic change is particularly common in populations of African descent, where the C allele is highly prevalent compared to other ancestries [4]. Because it modifies the metabolism of both sex hormones and therapeutic drugs, this variant has been linked to hormone-sensitive cancer risks and altered responses to several critical medications [5].
Key Insight: The CYP3A4*1B variant (C allele) is the minor allele globally but is actually the dominant major allele in populations of African descent. This variant can significantly increase the rate of metabolism for certain immunosuppressants, showing a reduced response to prevent organ transplant rejection.
Location: CYP3A4. Chromosome 7 · 7q22.1 · 99.8 Mb
Estimated prevalence by population
Global 11.5%; European 0.1%; African 41.1%; East Asian < 0.1%; South Asian 0.1%; Americas 1.3%; Ashkenazi 0.2%; Finnish 0.1%; Middle Eastern 0.6%; Amish 0.8%.
Estimated CC genotype frequency.
Global 18.9%; European 6.8%; African 46.0%; East Asian 0.4%; South Asian 5.9%; Americas 20.0%; Ashkenazi 8.9%; Finnish 7.1%; Middle Eastern 14.4%; Amish 16.2%.
Estimated CT genotype frequency.
Global 69.6%; European 93.1%; African 12.9%; East Asian 99.6%; South Asian 94.1%; Americas 78.7%; Ashkenazi 90.9%; Finnish 92.8%; Middle Eastern 85.0%; Amish 83.0%.
Estimated TT genotype frequency.
Showing effects for C/C genotype
Cancer & Oncology
Prostate Cancer
Prostate Cancer. Evidence: 4/10. Source: PMID 23179402. ~2.5x Increased Risk.
Gynecological Cancers
Ovarian Cancer. Evidence: 3/10. Source: PMID 23179402. ~2.5x Increased Risk.
Pharmacogenomics
Immunosuppressant & Biologic Response
Tacrolimus Clearance. Evidence: 6/10. Source: PMID 26039043. Faster Metabolism.
Chemotherapy Response
Cyclophosphamide Response. Evidence: 5/10. Source: PMID 20459744. Poorer Response.
Lipid-Lowering Drug Response
Atorvastatin Response. Evidence: 5/10. Source: PMID 39523378. Poorer Response.
Showing effects for C/T genotype
Prostate Cancer. Evidence: 4/10. Source: PMID 23179402. Typical Risk.
Ovarian Cancer. Evidence: 3/10. Source: PMID 23179402. Typical Risk.
Atorvastatin Response. Evidence: 5/10. Source: PMID 39523378. Typical Response.
Showing effects for T/T genotype
Tacrolimus Clearance. Evidence: 6/10. Source: PMID 26039043. Slower Metabolism.
Cyclophosphamide Response. Evidence: 5/10. Source: PMID 20459744. Typical Response.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Presence of two copies of the C allele (the CYP3A4*1B variant) is associated with an elevated risk of developing hormone-sensitive cancers. Meta-analyses show an approximately 2.5-fold increased risk for prostate and ovarian cancers among individuals with this genotype [1]. In African American populations, this variant is particularly common and has been linked to a higher risk of aggressive prostate cancer [2]. Beyond cancer susceptibility, this genotype leads to rapid clearance of the immunosuppressant drug tacrolimus, which significantly increases the risk of organ transplant rejection unless higher doses are administered [3]. It is also associated with a poorer therapeutic response to the chemotherapy drug cyclophosphamide [4] and the cholesterol-lowering medication atorvastatin [5].
Increased risk of prostate and ovarian cancers; Rapid clearance of tacrolimus, with lower blood levels; Reduced response to cyclophosphamide chemotherapy.
Sample genotype: CT (Heterozygous)
Inheriting a single copy of the C allele generally maintains a typical baseline risk for prostate and ovarian cancers, as the elevated risk is primarily observed in homozygous carriers [1]. However, this heterozygous genotype still has a profound impact on drug metabolism. Clinical studies show that individuals with this genotype clear the transplant drug tacrolimus much faster than non-carriers, which can elevate the risk of organ rejection if standard doses are used [2]. This genotype is also associated with a poorer response and reduced survival outcomes when treated with the chemotherapy agent cyclophosphamide [3]. Additionally, some chemotherapy regimens may carry an increased risk of side effects like hair loss for carriers of this variant [4].
Accelerated clearance of tacrolimus; Poorer response to cyclophosphamide chemotherapy; Typical baseline cancer risk.
Sample genotype: TT (Homozygous)
Two copies of the T allele represent the normal, wild-type state for the CYP3A4 gene. This genotype is associated with typical baseline risks for both prostate and ovarian cancers, avoiding the elevated risks linked to the variant form [1]. In the context of pharmacogenomics, individuals with this genotype exhibit standard or slower clearance rates for key medications. For example, patients taking the immunosuppressant tacrolimus reach therapeutic levels more readily, resulting in a decreased likelihood of organ transplant rejection [2]. It is also associated with a typical, expected response to chemotherapy drugs like cyclophosphamide [3] and statins like atorvastatin [4].
Typical baseline risk for prostate and ovarian cancers; Standard clearance of tacrolimus with lower rejection risk; Expected response to atorvastatin and cyclophosphamide.
Variants with shared genetic architecture
rs2242480 · CYP3A4 Gene · Chr 7 · Drug Metabolism and Heart Risk
rs35599367 · CYP3A4 Gene · Chr 7 · Medication Clearance Rate
rs4646437 · CYP3A4 Gene · Chr 7 · Drug Metabolism and Health
CYP3A4*1B polymorphism and cancer risk: a HuGE review and meta-analysis.
Polymorphisms in CYP17 and CYP3A4 and prostate cancer in men of African descent.
Content updated August 2026.
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