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Association of TP53 (rs1042522) and BRCA1 Gene Polymorphisms with the Pharmacokinetics of 5-Fluorouracil among Breast Cancer Patients in Southern Punjab, Pakistan: A Step Towards Precision Oncology

This study of 200 Pakistani breast cancer patients reveals that while individual TP53 and BRCA1 polymorphisms do not significantly alter 5-fluorouracil pharmacokinetics, specific combined BRCA1 haplotypes and occupational factors (such as housewifery) are associated with markedly elevated drug exposure and reduced clearance, supporting the integration of pharmacogenomic screening into precision oncology strategies for this population.

Original authors: Mehwish Sultana, Shanzay Imtiaz Malik, Sumera Malik, Ramsha Jan, Umm-e- Farwa, Javairia Saeed, Rashda Shabbir, Preza Kuinkel

Published 2026-08-10

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CC BY 4.0

Original authors: Mehwish Sultana, Shanzay Imtiaz Malik, Sumera Malik, Ramsha Jan, Umm-e- Farwa, Javairia Saeed, Rashda Shabbir, Preza Kuinkel

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your body as a bustling city where every drug you take is a delivery truck carrying a special package. Sometimes, the city's traffic lights and road conditions change how fast that truck gets to its destination. In the world of cancer treatment, one of the most common "delivery trucks" is a medicine called 5-Fluorouracil (or 5-FU for short). It's a powerful agent used to fight breast cancer, but it's a bit of a wild card. For some people, the truck moves too slowly, leaving the cancer cells unharmed; for others, it zooms in too fast and causes a traffic jam of side effects. Scientists have long known that our genes act like the city's blueprint, deciding how many traffic lights we have and how wide our roads are. Specifically, two genes—TP53 and BRCA1—are famous for their roles in keeping cells healthy and fixing DNA damage. But could these same genes also be the traffic controllers that decide how fast the 5-FU truck moves through the body? This is the question researchers in Pakistan set out to answer, hoping to turn cancer treatment from a "one-size-fits-all" guess into a precise, personalized plan.

In a study involving 200 breast cancer patients in Southern Punjab, researchers acted like detectives, tracking the journey of 5-FU through the patients' bodies while checking their genetic blueprints. They looked for specific variations, or "typos," in the TP53 and BRCA1 genes to see if these typos changed how the drug behaved. Think of the TP53 gene as a security guard who can either be very strict or a bit more relaxed, and the BRCA1 gene as a construction crew that builds the roads the drug travels on. The researchers found that looking at just one gene at a time didn't give them a clear answer; the traffic patterns were too messy to blame on a single blueprint. However, when they looked at the combination of genes—like checking both the security guard and the construction crew together—they spotted something fascinating. Patients with a specific combination of BRCA1 "typos" (the AA type) seemed to have a much slower traffic flow. Their bodies held onto the drug longer, with drug levels (measured as AUC) reaching as high as 149.8 µg•h/mL, compared to the usual range of 38.9 to 71.2 µg•h/mL for others. It was as if their internal roads were narrower, causing the drug trucks to pile up.

But the story didn't end with genes. The researchers discovered that the patients' daily lives were just as important as their DNA. They found that "occupation" and "childhood home" were massive factors. Women who worked as farmers or grew up in rural areas had drug levels that were significantly lower than housewives or those raised in cities. It turns out that years of exposure to farm pesticides might have "supercharged" the farmers' liver enzymes, making them incredibly efficient at cleaning the drug out of their system. In contrast, housewives and city-raised patients had much higher drug exposure, with clearance rates dropping to 17.5 L/h compared to 28.3 L/h for farmers. This suggests that the environment acts like a giant, invisible modifier of the genetic blueprint.

The study also looked at how these differences affected the patients' side effects. While everyone lost their hair (a 100% occurrence across all groups), those with the higher drug exposure (the farmers' city-dwelling counterparts and those with the specific BRCA1 combination) tended to report more stomach issues and pain. The researchers concluded that while the genes TP53 and BRCA1 play a role, they work best when viewed alongside environmental factors. They suggest that before giving 5-FU, doctors should check not just the patient's genes, but also their job history and where they grew up. This approach could help doctors adjust the dose so that the drug truck arrives at the cancer cells at the perfect speed—fast enough to do the job, but slow enough to avoid a crash. While the study suggests these findings are real, the authors note that the group of patients with the specific high-risk gene combination was small, so these results are a strong hint rather than a final proof, calling for more research to confirm the pattern.

Technical Summary: Association of TP53 (rs1042522) and BRCA1 Gene Polymorphisms with the Pharmacokinetics of 5-Fluorouracil among Breast Cancer Patients in Southern Punjab, Pakistan

Problem Statement
Breast cancer represents approximately 40% of all female malignancies in Pakistan, with a high prevalence of late-stage (II–III) presentation. The standard of care involves the FAC (5-Fluorouracil, Adriamycin, Cyclophosphamide) regimen. However, 5-Fluorouracil (5-FU) is characterized by a narrow therapeutic window and extreme inter-individual pharmacokinetic (PK) variability (up to 100-fold), leading to unpredictable therapeutic outcomes and dose-limiting toxicities. While polymorphisms in the DPYD gene are established determinants of 5-FU metabolism, they explain only a portion of the observed variability. This study addresses the gap in knowledge regarding whether germline polymorphisms in tumor suppressor genes TP53 (rs1042522; Arg72Pro) and BRCA1 (exon 11) modulate 5-FU systemic exposure in the Pakistani population, a demographic with unique genetic and environmental characteristics, including high consanguinity and extensive agricultural xenobiotic exposure.

Methodology
The study employed a prospective observational design involving 200 histologically confirmed breast cancer patients (Stage II–III) from Nishtar Hospital, Multan.

Genotyping: Genomic DNA was extracted using the phenol-chloroform-isoamyl alcohol method. TP53 (rs1042522) and BRCA1 (exon 11) genotypes were determined using a validated Tetra-Primer ARMS-PCR technique.
Pharmacokinetic Sampling: Patients received intravenous 5-FU as part of the FAC regimen. Plasma samples were collected at four time points (early distribution, steady-state, elimination, and post-infusion).
Quantification: Plasma 5-FU concentrations were quantified using a validated Reverse-Phase HPLC method (Shimadzu LC-10AT) with UV detection at 254 nm.
PK Analysis: Pharmacokinetic parameters ( $AUC_{0-t}$ , $C_{max}$ , $t_{1/2}$ , $CL$, $V_d$ , $T_{max}$ , $MRT$) were calculated using PK Solver software based on a one-compartment IV infusion model.
Statistical Analysis: Data were analyzed using non-parametric tests (Kruskal-Wallis, Mann-Whitney U) due to non-normal distribution. Multivariable linear regression was used to identify independent predictors of PK parameters, controlling for demographics and clinical covariates.

Key Results

Genotype Distribution: The study cohort showed TP53 genotype frequencies of GG (19.5%), GC (55.5%), and CC (25.0%), and BRCA1 frequencies of GG (30.5%), GA (64.0%), and AA (5.5%). Both loci were in Hardy-Weinberg Equilibrium.
Individual Genotype Associations: Analysis of individual genotypes revealed no statistically significant differences in 5-FU PK parameters across TP53 or BRCA1 groups alone. However, a trend was observed where TP53 GG carriers exhibited numerically higher exposure ( $AUC_{0-t}$ ) and lower clearance compared to GC/CC carriers.
Haplotype Analysis: A notable finding emerged from combined haplotype analysis, though the authors caution that small subgroup sizes limit statistical power. Patients carrying BRCA1 AA haplotypes (specifically TP53 GG + BRCA1 AA and TP53 CC + BRCA1 AA) demonstrated markedly elevated systemic exposure compared to non-AA haplotypes. The GG+AA haplotype showed a mean $AUC_{0-t}$ of 149.8 µg•h/mL and $C_{max}$ of 77.9 µg/mL, while the CC+AA haplotype showed 138.8 µg•h/mL and 59.2 µg/mL, respectively. Conversely, the GC+AA haplotype showed paradoxically lower exposure, suggesting a potential protective interaction. The authors note that while these differences were clinically substantial, they did not reach conventional statistical significance in the primary analysis due to the small size of the AA subgroup (n=11), rendering these findings hypothesis-generating.
Environmental and Occupational Modulators: Occupation and childhood residence were identified as significant independent predictors of 5-FU PK. Housewives exhibited significantly higher $AUC_{0-t}$ (128.3 vs. 39.3 µg•h/mL) and lower clearance compared to farming women. Similarly, patients raised in urban areas had higher exposure than those raised in rural areas. The authors attribute this to chronic pesticide exposure in agricultural workers inducing hepatic metabolic enzymes (e.g., CYPs), thereby enhancing 5-FU clearance.
Clinical Predictors: Multivariable regression identified Body Surface Area (BSA), cancer stage, and chemotherapy cycle as the strongest independent clinical predictors of 5-FU exposure.
Toxicity: Alopecia occurred in 100% of patients regardless of genotype. Trends suggested higher gastrointestinal toxicity in BRCA1 AA carriers, consistent with their higher drug exposure.

Significance and Claims
The paper claims to be the first systematic investigation into the association of TP53 and BRCA1 polymorphisms with 5-FU pharmacokinetics in Pakistani breast cancer patients. Its primary contributions are:

Identification of a Potential High-Risk Subgroup: The study suggests that BRCA1 AA-carrying haplotypes (particularly in combination with specific TP53 genotypes) may represent a pharmacokinetically distinct subgroup with elevated 5-FU exposure, which could predispose them to toxicity. The authors emphasize that these findings are hypothesis-generating and require validation in larger cohorts.
Environmental Pharmacogenomics: It highlights that occupational and environmental factors (specifically agricultural pesticide exposure) are potent, independent modulators of 5-FU pharmacokinetics in this population, potentially explaining variability that standard BSA-based dosing fails to capture.
Precision Oncology Strategy: The authors propose that pre-treatment risk stratification in South Asian populations should integrate pharmacogenomic profiling (TP53, BRCA1, and established DPYD testing) alongside occupational and environmental history. This approach aims to facilitate individualized dose adjustments, reduce toxicity burdens, and advance precision oncology.

The authors maintain a modest tone regarding the statistical significance of individual genotypes, noting that the study was not powered to detect modest effect sizes for single loci. They emphasize that the findings regarding BRCA1 AA haplotypes and environmental factors are hypothesis-generating and require prospective, multi-center validation with larger subgroup sizes and inclusion of DPYD genotyping.

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