Germline pharmacogenetics of paclitaxel for cancer treatment

CYP2C8 rs11572080 and CYP3A4 rs2740574 risk genotypes in paclitaxel-treated premenopausal breast cancer patients

Breast cancer (BC) is the most prevalent malignancy in women globally. At time of diagnosis, premenopausal BC is considered more aggressive and harder to treat than postmenopausal cases. Cytochrome P450 (CYP) enzymes are responsible for phase I of estrogen metabolism and thus, they are prominently involved in the pathogenesis of BC. Moreover, CYP subfamily 2C and 3A play a pivotal role in the metabolism of taxane anticancer agents. To understand genetic risk factors that may have a role in pre-menopausal BC we studied the genotypic variants of CYP2C8, rs11572080 and CYP3A4, rs2740574 in female BC patients on taxane-based therapy and their association with menopausal status. Our study comprised 105 female patients with histologically proven BC on paclitaxel-therapy. They were stratified into pre-menopausal (n = 52, 49.5%) and post-menopausal (n = 53, 50.5%) groups. Genotyping was done using TaqMan assays and employed on Quantstudio 12 K flex real-time platform. Significant increased frequencies of rs11572080 heterozygous CT genotype and variant T allele were established in pre-menopausal group compared to post-menopausal group (p = 0.023, 0.01, respectively). Moreover, logistic regression analysis revealed a significant association between rs11572080 CT genotype and premenopausal BC. However, regarding rs2740574, no significant differences in genotypes and allele frequencies between both groups were detected. We reported a significant association between CYP2C8 genotypic variants and premenopausal BC risk in Egyptian females. Further studies on larger sample sizes are still needed to evaluate its importance in early prediction of BC in young women and its effect on treatment outcome.

CYP3A genetic variation and taxane-induced peripheral neuropathy: a systematic review, meta-analysis, and candidate gene study

Background: Taxane-induced peripheral neuropathy (TIPN) is an important cause of premature treatment cessation and dose-limitation in cancer therapy. It also reduces quality of life and survivorship in affected patients. Genetic polymorphisms in the CYP3A family have been investigated but the findings have been inconsistent and contradictory. Methods: A systematic review identified 12 pharmacogenetic studies investigating genetic variation in CYP3A4*22 and CYP3A5*3 and TIPN. In our candidate gene study, 288 eligible participants (211 taxane participants receiving docetaxel or paclitaxel, and 77 control participants receiving oxaliplatin) were successfully genotyped for CYP3A4*22 and CYP3A5*3. Genotyping data was transformed into a combined CYP3A metaboliser phenotype: Poor metabolisers, intermediate metabolisers and extensive metabolisers. Individual genotypes and combined CYP3A metaboliser phenotypes were assessed in relation to neurotoxicity, including by meta-analysis where possible. Results: In the systematic review, no significant association was found between CYP3A5*3 and TIPN in seven studies, with one study reporting a protective association. For CYP3A4*22, one study has reported an association with TIPN, while four other studies failed to show an association. Evaluation of our patient cohort showed that paclitaxel was found to be more neurotoxic than docetaxel (p < 0.001). Diabetes was also significantly associated with the development of TIPN. The candidate gene analysis showed no significant association between either SNP (CYP3A5*3 and CYP3A4*22) and the development of TIPN overall, or severe TIPN. Meta-analysis showed no association between these two variants and TIPN. Transformed into combined CYP3A metaboliser phenotypes, 30 taxane recipients were poor metabolisers, 159 were intermediate metabolisers, and 22 were extensive metabolisers. No significant association was observed between metaboliser status and case-control status. Summary: We have shown that the risk of peripheral neuropathy during taxane chemotherapy is greater in patients who have diabetes. CYP3A genotype or phenotype was not identified as a risk factor in either the candidate gene analysis or the systematic review/meta-analysis, although we cannot exclude the possibility of a minor contribution, which would require a larger sample size.

Pharmacogenomics in Cytotoxic Chemotherapy of Cancer

Pharmacogenetic testing in patients with cancer requiring cytotoxic chemotherapy offers the potential to predict, prevent, and mitigate chemotherapy-related toxicities. While multiple drug-gene pairs have been identified and studied, few drug-gene pairs are currently used routinely in the clinical status. Here we review what is known, theorized, and unknown regarding the use of pharmacogenetic testing in cancer.

Current opinion on the pharmacogenomics of paclitaxel-induced toxicity

Introduction: Paclitaxel is a microtubule stabilizer that is currently one of the most utilized chemotherapeutic agents. Its efficacy in breast, uterine, lung and other neoplasms made its safety profile enhancement a subject of great interest. Neurotoxicity is the most common paclitaxel-associated toxicities. In addition, hypersensitivity reactions, hematological, gastrointestinal, and cardiac toxicities are all encountered.Areas covered: The current review explores paclitaxel-induced toxicities mechanisms and risk factors. Studies investigating these toxicities pharmacogenomic biomarkers are reviewed and summarized. There is a limited margin of consistency between the retrieved associations. Variants in genes related to neuro-sensitivity are the most promising candidates for future studies.Expert opinion: Genome-wide association studies highlighted multiple-candidate biomarkers relevant to neuro-sensitivity. Most of the identified paclitaxel-neurotoxicity candidate genes are derived from congenital neuropathy and diabetic-induced neurotoxicity pathways. Future studies should explore these sets of genes while considering the multifactorial nature of paclitaxel-induced neurotoxicity. In the absence of certain paclitaxel-toxicity biomarkers, future research should avoid earlier studies' caveats. Genes in paclitaxel's pharmacokinetic pathways could not provide consistent results in any of its associated toxicities. There is a need to dig deeper into toxicity-development mechanisms and personal vulnerability factors, rather than targeting only the genes suspected to affect drug exposure.

Nobiletin downregulates the SKP2-p21/p27-CDK2 axis to inhibit tumor progression and shows synergistic effects with palbociclib on renal cell carcinoma

Objective:

Natural extracts, including nobiletin, have been reported to enhance the efficacy and sensitivity of chemotherapeutic drugs. However, whether and how nobiletin affects tumor growth and progression in renal cell carcinoma (RCC) are still unclear.

Methods:

Cell proliferation, cell cycle and apoptosis analyses, colony-formation assays, immunoblotting analysis, and qRT-PCR analysis were performed to investigate how nobiletin affected RCC cell proliferation in vitro. The nude mouse model was used to test the efficacy of nobiletin alone or in combination with palbociclib.

Results:

Nobiletin inhibited cell proliferation by inducing G1 cell cycle arrest and cell apoptosis in RCC cells. Mechanistically, nobiletin decreased SKP2 protein expression by reducing its transcriptional level. The downregulated SKP2 caused accumulation of its substrates, p27 and p21, which further inhibited the activity of the G1 phase-related protein, CDK2, leading to inhibition of cell proliferation and tumor formation. A higher SKP2 protein level indicated less sensitivity to the CDK4/6 inhibitor, palbociclib. A combination of nobiletin and palbociclib showed a synergistic tumor inhibition in vitro and in an in vivo model.

Conclusions:

Nobiletin downregulated the SKP2-p21/p27-CDK2 axis to inhibit tumor progression and showed synergistic tumor inhibition effects with the CDK4/6 inhibitor, palbociclib, on RCC, which indicates a potential new therapeutic strategy.

Exploring pharmacogenetics of paclitaxel- and docetaxel-induced peripheral neuropathy by evaluating the direct pharmacogenetic-pharmacokinetic and pharmacokinetic-neuropathy relationships

Introduction: Peripheral neuropathy (PN) is an adverse effect of several classes of chemotherapy including the taxanes. Predictive PN biomarkers could inform individualized taxane treatment to reduce PN and enhance therapeutic outcomes. Pharmacogenetics studies of taxane-induced PN have focused on genes involved in pharmacokinetics, including enzymes and transporters. Contradictory findings from these studies prevent translation of genetic biomarkers into clinical practice. Areas covered: This review discusses the progress toward identifying pharmacogenetic predictors of PN by assessing the evidence for two independent associations; the effect of pharmacogenetics on taxane pharmacokinetics and the evidence that taxane pharmacokinetics affects PN. Assessing these direct relationships allows the reader to understand the progress toward individualized taxane treatment and future research opportunities. Expert opinion: Paclitaxel pharmacokinetics is a major determinant of PN. Additional clinical trials are needed to confirm the clinical benefit of individualized dosing to achieve target paclitaxel exposure. Genetics does not meaningfully contribute to paclitaxel pharmacokinetics and may not be useful to inform dosing. However, genetics may contribute to PN sensitivity and could be useful for estimating patients' optimal paclitaxel exposure. For docetaxel, genetics has not been demonstrated to have a meaningful effect on pharmacokinetics and there is no evidence that pharmacokinetics determines PN.

Weekly Carboplatin and Paclitaxel: A Retrospective Comparison with the Three-Weekly Schedule in First-Line Treatment of Ovarian Cancer

BACKGROUND

Conventional first-line combination therapy for ovarian cancer comprises 6 cycles of adjuvant or neoadjuvant carboplatin (AUC5-6) with paclitaxel (175 mg/m² ) every 3 weeks (PC-3W). Weekly scheduling of paclitaxel may maximize its antiangiogenic effect and reduce adverse effects. We compared the efficacy and safety of PC-3W with a modified protocol of weekly paclitaxel 80 mg/m² and weekly carboplatin AUC2 administered on days 1, 8, and 15 in a 28-day cycle (i.e., with 1 week off-treatment [PC-W]).

MATERIALS AND METHODS

Medical records of consecutive patients treated between 2000 and 2018 were reviewed; 707 patients were analyzed for demographic and clinical characteristics, effectiveness and toxicity.

RESULTS

PC-3W was administered to 402 patients (median age, 60.5 years) and PC-W to 305 patients (median age, 62.5 years). Most patients (91.4%) were diagnosed at stage III-IV. Notwithstanding a higher proportion of residual disease and older patients in the PC-W group, median progression-free survival was 21.4 months and 13.2 months for PC-W and PC-3W, respectively; median overall survival was 75.2 and 54.0 months for PC-W and PC-3W, respectively. Cox proportional hazards model indicated improved survival for patients treated with PC-W (hazard ratio, 0.54). Similar results were observed for older patients diagnosed at ≥75 years. PC-W demonstrated a better safety profile, with lower incidence of neuropathy, neutropenia, and alopecia.

CONCLUSION

PC-W is as active and better tolerated than the standard PC-3W regimen. PC-W may serve as an alternative option for elderly or frail patients.

IMPLICATIONS FOR PRACTICE

Weekly scheduling of paclitaxel 80 mg/m² and carboplatin AUC2, administered on days 1, 8, and 15 in a 28-day cycle (PC-W) for first-line therapy for advanced ovarian cancer, is as active and better tolerated than the standard regimen of carboplatin and paclitaxel (175 mg/m² ) every 3 weeks (PC-3W). It is possible that the weekly holiday on day 21 in the PC-W regimen may ensure better completion rates (which may result in treatment delays for toxicity in PC-3W). The results of this retrospective analysis highlight the weekly regimen as a valid treatment option, especially for elderly patients and those with significant comorbidities.

Solute Carrier Transportome in Chemotherapy-Induced Adverse Drug Reactions

Members of the solute carrier (SLC) family of transporters are responsible for the cellular influx of a broad range of endogenous compounds and xenobiotics. These proteins are highly expressed in the gastrointestinal tract and eliminating organs such as the liver and kidney, and are considered to be of particular importance in governing drug absorption and elimination. Many of the same transporters are also expressed in a wide variety of organs targeted by clinically important anticancer drugs, directly affect cellular sensitivity to these agents, and indirectly influence treatment-related side effects. Furthermore, targeted intervention strategies involving the use of transport inhibitors have been recently developed, and have provided promising lead candidates for combinatorial therapies associated with decreased toxicity. Gaining a better understanding of the complex interplay between transporter-mediated on-target and off-target drug disposition will help guide the further development of these novel treatment strategies to prevent drug accumulation in toxicity-associated organs, and improve the safety of currently available treatment modalities. In this report, we provide an update on this rapidly emerging field with particular emphasis on anticancer drugs belonging to the classes of taxanes, platinum derivatives, nucleoside analogs, and anthracyclines.

Weekly versus 3-weekly paclitaxel in combination with carboplatin in advanced ovarian cancer: which is the optimal adjuvant chemotherapy regimen?

The 3-weekly regimen of carboplatin and paclitaxel is the backbone of first line adjuvant chemotherapy for advanced ovarian cancer. The landmark Japanese Gynaecologic Oncology Group (JGOG) 3016 study demonstrated significant improvements in progression-free survival and overall survival with dose dense weekly administration of paclitaxel in combination with 3-weekly carboplatin. However, efforts to replicate these benefits have failed in subsequent phase III trials. Weekly paclitaxel is purported to have enhanced antitumor activity, with stronger anti-angiogenic effects, and yet is better tolerated. In this review, we explore the rationale for dose dense weekly paclitaxel, and compare the relevant trials as well as quality of life considerations. Possible reasons for the difference in outcomes between the JGOG 3016 and other studies are reviewed, with a focus on how the addition of bevacizumab, the variations between histological and molecular subtypes of epithelial ovarian cancers, and ethnic pharmacogenetic differences may potentially affect the efficacy of dose dense paclitaxel.

Germline genetic variants with implications for disease risk and therapeutic outcomes

Genetic testing has multiple clinical applications including disease risk assessment, diagnosis, and pharmacogenomics. Pharmacogenomics can be utilized to predict whether a pharmacologic therapy will be effective or to identify patients at risk for treatment-related toxicity. Although genetic tests are typically ordered for a distinct clinical purpose, the genetic variants that are found may have additional implications for either disease or pharmacology. This review will address multiple examples of germline genetic variants that are informative for both disease and pharmacogenomics. The discussed relationships are diverse. Some of the agents are targeted for the disease-causing genetic variant, while others, although not targeted therapies, have implications for the disease they are used to treat. It is also possible that the disease implications of a genetic variant are unrelated to the pharmacogenomic implications. Some of these examples are considered clinically actionable pharmacogenes, with evidence-based, pharmacologic treatment recommendations, while others are still investigative as areas for additional research. It is important that clinicians are aware of both the disease and pharmacogenomic associations of these germline genetic variants to ensure patients are receiving comprehensive personalized care.

SNPs associated with activity and toxicity of cabazitaxel in patients with advanced urothelial cell carcinoma

AIM

We aimed to identify SNPs associated with cabazitaxel toxicity and response within a Phase II clinical trial using this compound in advanced transitional cell carcinoma after progression to a platinum-based regimen.

PATIENTS & METHODS

Eleven SNPs in CYP3A4, CYP3A5, CYP2C8, ABCB1 and TUBB1 were genotyped in 45 patients.

RESULTS

CYP3A5 rs776746 A allele was associated with protection against gastrointestinal toxicity (odds ratio: 0.06, 95% CI: 0.007-0.63, p = 0.018) and with reduced progression-free survival (hazard ratio: 5.1, 95% CI: 1.7-15.1, p = 0.0038, multivariable analysis). ABCB1 SNPs were associated with total number of grade 3-4 toxicity events (p-values of 0.009, 0.041 and 0.043, respectively).

CONCLUSION

Polymorphisms in CYP3A5 and ABCB1 may define a subset of patients with different cabazitaxel toxicity and efficacy and therefore could be used as markers for treatment optimization.

Weekly vs. Every-3-Week Paclitaxel and Carboplatin for Ovarian Cancer

BACKGROUND

A dose-dense weekly schedule of paclitaxel (resulting in a greater frequency of drug delivery) plus carboplatin every 3 weeks or the addition of bevacizumab to paclitaxel and carboplatin administered every 3 weeks has shown efficacy in ovarian cancer. We proposed to determine whether dose-dense weekly paclitaxel and carboplatin would prolong progression-free survival as compared with paclitaxel and carboplatin administered every 3 weeks among patients receiving and those not receiving bevacizumab.

METHODS

We prospectively stratified patients according to whether they elected to receive bevacizumab and then randomly assigned them to receive either paclitaxel, administered intravenously at a dose of 175 mg per square meter of body-surface area every 3 weeks, plus carboplatin (dose equivalent to an area under the curve [AUC] of 6) for six cycles or paclitaxel, administered weekly at a dose of 80 mg per square meter, plus carboplatin (AUC, 6) for six cycles. The primary end point was progression-free survival.

RESULTS

A total of 692 patients were enrolled, 84% of whom opted to receive bevacizumab. In the intention-to-treat analysis, weekly paclitaxel was not associated with longer progression-free survival than paclitaxel administered every 3 weeks (14.7 months and 14.0 months, respectively; hazard ratio for disease progression or death, 0.89; 95% confidence interval [CI], 0.74 to 1.06; P=0.18). Among patients who did not receive bevacizumab, weekly paclitaxel was associated with progression-free survival that was 3.9 months longer than that observed with paclitaxel administered every 3 weeks (14.2 vs. 10.3 months; hazard ratio, 0.62; 95% CI, 0.40 to 0.95; P=0.03). However, among patients who received bevacizumab, weekly paclitaxel did not significantly prolong progression-free survival, as compared with paclitaxel administered every 3 weeks (14.9 months and 14.7 months, respectively; hazard ratio, 0.99; 95% CI, 0.83 to 1.20; P=0.60). A test for interaction that assessed homogeneity of the treatment effect showed a significant difference between treatment with bevacizumab and without bevacizumab (P=0.047). Patients who received weekly paclitaxel had a higher rate of grade 3 or 4 anemia than did those who received paclitaxel every 3 weeks (36% vs. 16%), as well as a higher rate of grade 2 to 4 sensory neuropathy (26% vs. 18%); however, they had a lower rate of grade 3 or 4 neutropenia (72% vs. 83%).

CONCLUSIONS

Overall, weekly paclitaxel, as compared with paclitaxel administered every 3 weeks, did not prolong progression-free survival among patients with ovarian cancer. (Funded by the National Cancer Institute and Genentech; GOG-0262 ClinicalTrials.gov number, NCT01167712.).

Pharmacogenetics of cancer therapy: breakthroughs from beyond?

‘Pharmacogenetics or Pharmacogenomics’ (PG) is one of the most practiced cancer therapeutic strategies, tailored for individualized patients. Despite its popularity and rapid advancements in the field, many obstacles for cancer therapy PG still need to be overcome. By borrowing scientific systems from other disciplines such as cancer diagnosis, and therapeutic information from the diversity of tumor origins, categories and stages, cancer therapy PG may hopefully be improved. Furthermore, to quickly acquire genetic and pathologic information and seek therapeutic interventions, possible breakthroughs may come from beyond – changing the cancer therapeutic landscapes. The next generations of PG protocols and hospital routines for searching deadly cancer pathogenic pathways versus drug-targeting predictions are of great clinical significance for the future. Yet, progress of cancer therapy PG is entering into a bottleneck stage owing to simple model of relevant techniques and routines. Promoting or even innovating present PG modular is very necessary. This perspective highlights this issue by introducing new initiatives and ideas.

SNPs and taxane toxicity in breast cancer patients

AIM

In order to identify genetic variants associated with taxanes toxicity, a panel with 47 SNPs in 20 genes involved in taxane pathways was designed.

PATIENTS & METHODS

Genomic DNA of 113 breast cancer patients was analyzed (70 taking docetaxel, 43 taking paclitaxel).

RESULTS

Two SNPs associated with docetaxel toxicity were identified: CYP3A4*1B with infusion-related reactions; and ERCC1 Gln504Lys with mucositis (p≤0.01). Regarding paclitaxel toxicity: CYP2C8 HapC and CYP2C8 rs1934951 were associated with anemia; and ERCC1 Gln504Lys with neuropathy (p≤0.01).

CONCLUSION

Genes involved in DNA repair mechanisms and reactive oxygen species levels influence taxane toxicity in cancer patients treated with chemotherapy schemes not containing platinum. These findings could lead to better treatment selection for breast cancer patients.

Predicting paclitaxel-induced neutropenia using the DMET platform

AIM

The use of paclitaxel in cancer treatment is limited by paclitaxel-induced neutropenia. We investigated the ability of genetic variation in drug-metabolizing enzymes and transporters to predict hematological toxicity.

PATIENTS & METHODS

Using a discovery and validation approach, we identified a pharmacogenetic predictive model for neutropenia. For this, a drug-metabolizing enzymes and transporters plus DNA chip was used, which contains 1936 SNPs in 225 metabolic enzyme and drug-transporter genes.

RESULTS

Our 10-SNP model in 279 paclitaxel-dosed patients reached 43% sensitivity in the validation cohort. Analysis in 3-weekly treated patients only resulted in improved sensitivity of 79%, with a specificity of 33%. None of our models reached statistical significance.

CONCLUSION

Our drug-metabolizing enzymes and transporters-based SNP-models are currently of limited value for predicting paclitaxel-induced neutropenia in clinical practice. Original submitted 9 March 2015; Revision submitted 20 May 2015.

Using drug response data to identify molecular effectors, and molecular "omic" data to identify candidate drugs in cancer

The current convergence of molecular and pharmacological data provides unprecedented opportunities to gain insights into the relationships between the two types of data. Multiple forms of large-scale molecular data, including but not limited to gene and microRNA transcript expression, DNA somatic and germline variations from next-generation DNA and RNA sequencing, and DNA copy number from array comparative genomic hybridization are all potentially informative when one attempts to recognize the panoply of potentially influential events both for cancer progression and therapeutic outcome. Concurrently, there has also been a substantial expansion of the pharmacological data being accrued in a systematic fashion. For cancer cell lines, the National Cancer Institute cell line panel (NCI-60), the Cancer Cell Line Encyclopedia (CCLE), and the collaborative Genomics of Drug Sensitivity in Cancer (GDSC) databases all provide subsets of these forms of data. For the patient-derived data, The Cancer Genome Atlas (TCGA) provides analogous forms of genomic information along with treatment histories. Integration of these data in turn relies on the fields of statistics and statistical learning. Multiple algorithmic approaches may be chosen, depending on the data being considered, and the nature of the question being asked. Combining these algorithms with prior biological knowledge, the results of molecular biological studies, and the consideration of genes as pathways or functional groups provides both the challenge and the potential of the field. The ultimate goal is to provide a paradigm shift in the way that drugs are selected to provide a more targeted and efficacious outcome for the patient.

NCI-60 whole exome sequencing and pharmacological CellMiner analyses

Exome sequencing provides unprecedented insights into cancer biology and pharmacological response. Here we assess these two parameters for the NCI-60, which is among the richest genomic and pharmacological publicly available cancer cell line databases. Homozygous genetic variants that putatively affect protein function were identified in 1,199 genes (approximately 6% of all genes). Variants that are either enriched or depleted compared to non-cancerous genomes, and thus may be influential in cancer progression and differential drug response were identified for 2,546 genes. Potential gene knockouts are made available. Assessment of cell line response to 19,940 compounds, including 110 FDA-approved drugs, reveals ≈80-fold range in resistance versus sensitivity response across cell lines. 103,422 gene variants were significantly correlated with at least one compound (at p<0.0002). These include genes of known pharmacological importance such as IGF1R, BRAF, RAD52, MTOR, STAT2 and TSC2 as well as a large number of candidate genes such as NOM1, TLL2, and XDH. We introduce two new web-based CellMiner applications that enable exploration of variant-to-compound relationships for a broad range of researchers, especially those without bioinformatics support. The first tool, “Genetic variant versus drug visualization”, provides a visualization of significant correlations between drug activity-gene variant combinations. Examples are given for the known vemurafenib-BRAF, and novel ifosfamide-RAD52 pairings. The second, “Genetic variant summation” allows an assessment of cumulative genetic variations for up to 150 combined genes together; and is designed to identify the variant burden for molecular pathways or functional grouping of genes. An example of its use is provided for the EGFR-ERBB2 pathway gene variant data and the identification of correlated EGFR, ERBB2, MTOR, BRAF, MEK and ERK inhibitors. The new tools are implemented as an updated web-based CellMiner version, for which the present publication serves as a compendium.

Genetic heterogeneity beyond CYP2C8*3 does not explain differential sensitivity to paclitaxel-induced neuropathy

The development of paclitaxel-induced peripheral neuropathy (PIPN) is influenced by drug exposure and patient genetics. The purpose of this analysis was to expand on a previous reported association of CYP2C8*3 and PIPN risk by investigating additional polymorphisms in CYP2C8 and in hundreds of other genes potentially relevant to paclitaxel pharmacokinetics. Clinical data was collected prospectively in an observational registry of newly diagnosed breast cancer patients. Patients treated with paclitaxel-containing regimens were genotyped using the Affymetrix DMET™ Plus chip. Patients who carried the CYP2C8*2, *3, or *4 variant were collapsed into a low-metabolizer CYP2C8 phenotype for association with PIPN. Separately, all SNPs that surpassed quality control were assessed individually and as a composite of genetic ancestry for associations with PIPN. 412 paclitaxel-treated patients and 564 genetic markers were included in the analysis. The risk of PIPN was significantly greater in the CYP2C8 low-metabolizer group (HR = 1.722, p = 0.018); however, the influences of the *2 and *4 SNPs were not independently significant (*2: p = 0.847, *4: p = 0.408). One intronic SNP in ABCG1 (rs492338) surpassed the exploratory significance threshold for an association with PIPN in the Caucasian cohort (p = 0.0008) but not in the non-Caucasian replication group (p = 0.54). Substantial genetic variability was observed within self-reported racial groups but this genetic variability was not associated with risk of grade 2+ PIPN. The pharmacogenetic heterogeneity within a cohort of breast cancer patients is dramatic, though we did not find evidence that this heterogeneity directly influences the risk of PIPN beyond the contribution of CYP2C8*3.