What you carry at this position in your DNA and what research says about it.
Chemotherapy Response: 5/10 evidence, 5 publications.
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Sample genotype (not yours): C/C
Typical Chemotherapy Response and Side Effect Risk
This genotype is associated with standard P-glycoprotein transporter activity. It represents the typical baseline response and side effect profile for various chemotherapy drugs.
What this genotype means: Standard drug transport; Typical chemotherapy side effect profile.
Sample genotype (not yours): C/T
Altered Chemotherapy Response and Mixed Treatment Outcomes
This genotype is linked to poorer response to some chemotherapies but better survival with specific myeloma treatments. It also increases the risk of certain treatment-related side effects.
What this genotype means: Altered drug transport efficiency; Increased risk of chemotherapy-induced diarrhea and vomiting; Potentially improved survival with lenalidomide and dexamethasone.
Sample genotype (not yours): T/T
This extremely rare genotype is expected to show altered drug transport, leading to drug-specific changes in chemotherapy response and side effects.
Gene function and biological role
Gene Function: The ABCB1 gene encodes P-glycoprotein, a vital cellular efflux pump that transports various substances out of cells [1]. This transporter is highly active in the gut, liver, kidneys, and the blood-brain barrier, where it helps protect tissues from toxins [1]. P-glycoprotein also plays a major role in determining how the body processes and eliminates many common medications, including chemotherapy drugs [2]. Variations in this gene can alter the pump's efficiency, leading to differences in drug accumulation and effectiveness [2].
Variant Impact: This missense variant, also known as Ser400Asn or 1199C>T, changes the amino acid serine to asparagine at position 400 of the P-glycoprotein transporter. Located in a cytoplasmic loop involved in substrate recognition, this alteration can modify how effectively the pump binds and exports specific drugs. Clinical studies show that this change does not cause any standalone genetic disorders, meaning it is considered benign for disease risk. However, it significantly influences the pharmacokinetics and toxicity profiles of several oncology treatments [3] [4].
Key Insight: This variant can make some cancer drugs less effective while actually improving survival outcomes for others.
Location: ABCB1. Chromosome 7 · 7q21.12 · 87.6 Mb
Estimated prevalence by population
Global 95.0%; European 92.1%; African 98.6%; East Asian 100.0%; South Asian 97.6%; Americas 94.5%; Ashkenazi 94.5%; Finnish 97.0%; Middle Eastern 92.7%; Amish 89.5%.
Estimated CC genotype frequency.
Global 4.9%; European 7.7%; African 1.4%; East Asian 0.0%; South Asian 2.4%; Americas 5.4%; Ashkenazi 5.4%; Finnish 3.0%; Middle Eastern 7.2%; Amish 10.2%.
Estimated CT genotype frequency.
Global 0.1%; European 0.2%; African < 0.1%; East Asian 0.0%; South Asian < 0.1%; Americas 0.1%; Ashkenazi 0.1%; Finnish < 0.1%; Middle Eastern 0.1%; Amish 0.3%.
Estimated TT genotype frequency.
Showing effects for C/C genotype
Pharmacogenomics
Chemotherapy Response
Chemotherapy Response. Evidence: 5/10. Source: PMID 25582575. Typical Response.
Chemotherapy Toxicity. Evidence: 5/10. Source: PMID 25637052. Typical Risk.
Cancer & Oncology
Cancer Prognosis & Treatment Outcome
Myeloma Survival. Evidence: 5/10. Source: PMID 29177954. Typical Survival.
Showing effects for C/T genotype
Chemotherapy Response. Evidence: 5/10. Source: PMID 25582575. Poorer Response.
Chemotherapy Toxicity. Evidence: 5/10. Source: PMID 25637052. Increased Risk.
Myeloma Survival. Evidence: 5/10. Source: PMID 29177954. Increased Survival.
Showing effects for T/T genotype
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Carrying two copies of the common C allele results in standard P-glycoprotein function. Individuals with this genotype generally experience typical absorption, distribution, and elimination of many medications [1]. In clinical studies of childhood acute lymphoblastic leukemia, this baseline function is associated with standard treatment outcomes when using drugs like vincristine and doxorubicin [1]. Similarly, patients undergoing R-CHOP therapy for lymphoma show typical rates of treatment-related side effects such as diarrhea and vomiting [2]. For multiple myeloma treatments involving lenalidomide, this genotype is linked to standard survival rates [3].
Standard drug transport; Typical chemotherapy side effect profile.
Sample genotype: CT (Heterozygous)
Carrying one copy of the T allele alters the substrate-binding region of the P-glycoprotein transporter. In pediatric leukemia treatments, this change is associated with a poorer response to medications like vincristine, doxorubicin, methotrexate, and prednisolone [1]. Patients receiving R-CHOP regimens for non-Hodgkin lymphoma also show an increased risk of experiencing side effects such as diarrhea and vomiting [2]. Conversely, in multiple myeloma patients treated with lenalidomide and dexamethasone, this genotype is linked to an increased likelihood of survival [3]. These contrasting outcomes highlight how a single genetic change can have highly drug-specific effects.
Altered drug transport efficiency; Increased risk of chemotherapy-induced diarrhea and vomiting; Potentially improved survival with lenalidomide and dexamethasone.
Sample genotype: TT (Homozygous)
Carrying two copies of the rare T allele is highly uncommon, occurring in less than one in a thousand individuals globally. While direct clinical data for this specific homozygous genotype are limited, it is expected to mirror or potentially amplify the effects seen in single-copy carriers. This includes a potentially poorer response to standard leukemia therapies such as vincristine and methotrexate [1]. It may also elevate the risk of gastrointestinal side effects like diarrhea and vomiting during R-CHOP chemotherapy [2]. However, based on related clinical trials, it might also correlate with improved survival outcomes when using lenalidomide-based regimens for multiple myeloma [3].
Variants with shared genetic architecture
rs1045642 · ABCB1 Gene · Chr 7 · Medication Response
rs2032582 · ABCB1 Gene · Chr 7 · Lung Cancer Risk
rs1128503 · ABCB1 Gene · Chr 7 · Medication Response
Genotyping panel for assessing response to cancer chemotherapy.
Content updated August 2026.
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