CYP2C8 rs1934951 — Paclitaxel Toxicity and Bone Drug Risk
CYP2C8 is one of the liver's key drug-metabolizing enzymes, responsible for breaking down a broad range of therapeutics including paclitaxel (a widely used chemotherapy agent), thiazolidinedione diabetes drugs, and antimalarials. Beyond drug metabolism, CYP2C8 converts arachidonic acid into epoxyeicosatrienoic acids 11 EETs: lipid mediators with vasodilatory and anti-inflammatory properties, meaning it plays a role in vascular regulation and inflammation even in people who never take any of its substrate drugs.
rs1934951 is an intronic variant22 Intronic: located within a non-coding region between two exons of the CYP2C8 gene in CYP2C8 that has attracted attention primarily in two clinical contexts: bisphosphonate-related osteonecrosis of the jaw (MRONJ) in cancer patients, and taxane-induced peripheral toxicity in chemotherapy recipients.
The Mechanism
The rs1934951 T allele (reported as the A allele in papers using the coding strand, since CYP2C8 is on the minus strand of chromosome 10) falls within intron 9 of CYP2C8 at position c.1291+106. As an intronic variant with no direct protein-coding effect, its functional mechanism is not fully established. Bisphosphonates are not CYP2C8 substrates per se, but CYP2C8-driven EET signaling influences osteoclast33 Osteoclasts: bone-resorbing cells regulated in part by EET lipid mediators activity and bone microvasculature, providing a plausible biological link.
The Evidence
The original finding came from a genome-wide association study in multiple
myeloma patients44 genome-wide association study in multiple
myeloma patients
Sarasquete ME et al. Bisphosphonate-related osteonecrosis of
the jaw associated with CYP2C8 polymorphisms. Blood, 2008
receiving bisphosphonates. In 22 cases of jaw osteonecrosis versus 65 matched
controls, the T allele (papers call it A) was dramatically overrepresented in
cases (48% vs 12%), with the odds ratio calculated assuming a dominant model of inheritance
(OR 12.75, 95% CI 3.7–43.5, p-corrected = 0.02). A meta-analysis by
Zhong et al. (2013)55 Zhong et al. (2013)
Zhong DN et al. CYP2C8 rs1934951 polymorphism meta-analysis.
Acta Haematol, 2013 found the
association held specifically in multiple myeloma patients (dominant model OR
5.77, p=0.028) but not across other cancer types.
However, a comprehensive review by Yang et al. (2019)66 Yang et al. (2019)
Yang G et al.
Pharmacogenomics of osteonecrosis of the jaw. Bone, 2019
concluded that all six subsequent candidate-gene replication studies failed to
confirm this association, attributing the original signal to the small sample
size of the discovery GWAS. The MRONJ association must therefore be treated as
an initial discovery finding that has not been independently validated.
The chemotherapy toxicity evidence is more consistent. A study of 113 breast
cancer patients found rs1934951 significantly associated with paclitaxel-induced
anemia (p≤0.01), in conjunction with CYP2C8 haplotype C
Boso et al. 201477 Boso et al. 2014
Bosó V et al. SNPs and taxane toxicity in breast cancer patients.
Pharmacogenomics, 2014. A more
recent multicenter cohort study of 130 ovarian cancer survivors (median 63-month
follow-up after chemotherapy) found that T-allele carriers had approximately
2.5-fold increased odds of experiencing severe long-term chemotherapy-induced
peripheral neuropathy (OR 2.482, 95% CI 1.13–5.47, p=0.024)
Zenatri et al. 202488 Zenatri et al. 2024
Zenatri M et al. Pharmacogenomic predictor of long-term
residual CIPN in ovarian cancer survivors. Gynecol Oncol, 2024.
Practical Actions
For individuals who may receive or are considering paclitaxel-based chemotherapy (used in breast, ovarian, lung, and other cancers), T-allele carriers — especially TT homozygotes — should discuss their genotype with their oncologist. Preventive neuropathy management strategies (such as dose modification, cold-cap gloves during infusion, and early physical therapy) are most effective when implemented proactively. For those receiving bisphosphonates (zoledronic acid, pamidronate) for bone protection or myeloma treatment, the MRONJ association remains biologically plausible but replication data is inconsistent; basic dental hygiene protocols before starting bisphosphonate therapy are standard of care for all patients regardless of genotype.
Interactions
The interaction between CYP2C8 metabolizer status and paclitaxel dose intensity has not yet been formalized into CPIC or DPWG guidelines, but multiple independent signals in the same gene strengthen the biological rationale.