Impact of CYP2D6 polymorphism on tamoxifen therapy: where are we?

Consensus statement for non-hormonal-based treatments for menopausal symptoms

Since the June 2014 consensus statement published in Post Reproductive Health we have had definitive guidelines on menopause treatment from the National Institute for Clinical Excellence in November 2015. These included robust and evidence based information about many non-estrogen based treatments, which are particularly useful for patients who do not wish to take hormone replacement therapy, or who have medical contraindications to hormonal therapy such as hormone dependent cancers. Whilst none of these therapies is as effective as hormones, we must be able to advise patients about them and recommend which treatments may be helpful for individual women.

Tamoxifen induces a pluripotency signature in breast cancer cells and human tumors

Tamoxifen is the treatment of choice in estrogen receptor alpha breast cancer patients that are eligible for adjuvant endocrine therapy. However, ∼50% of ERα-positive tumors exhibit intrinsic or rapidly acquire resistance to endocrine treatment. Unfortunately, prediction of de novo resistance to endocrine therapy and/or assessment of relapse likelihood remain difficult. While several mechanisms regulating the acquisition and the maintenance of endocrine resistance have been reported, there are several aspects of this phenomenon that need to be further elucidated. Altered metabolic fate of tamoxifen within patients and emergence of tamoxifen-resistant clones, driven by evolution of the disease phenotype during treatment, appear as the most compelling hypotheses so far. In addition, tamoxifen was reported to induce pluripotency in breast cancer cell lines, in vitro. In this context, we have performed a whole transcriptome analysis of an ERα-positive (T47D) and a triple-negative breast cancer cell line (MDA-MB-231), exposed to tamoxifen for a short time frame (hours), in order to identify how early pluripotency-related effects of tamoxifen may occur. Our ultimate goal was to identify whether the transcriptional actions of tamoxifen related to induction of pluripotency are mediated through specific ER-dependent or independent mechanisms. We report that even as early as 3 hours after the exposure of breast cancer cells to tamoxifen, a subset of ERα-dependent genes associated with developmental processes and pluripotency are induced and this is accompanied by specific phenotypic changes (expression of pluripotency-related proteins). Furthermore we report an association between the increased expression of pluripotency-related genes in ERα-positive breast cancer tissues samples and disease relapse after tamoxifen therapy. Finally we describe that in a small group of ERα-positive breast cancer patients, with disease relapse after surgery and tamoxifen treatment, ALDH1A1 (a marker of pluripotency in epithelial cancers which is absent in normal breast tissue) is increased in relapsing tumors, with a concurrent modification of its intra-cellular localization. Our data could be of value in the discrimination of patients susceptible to develop tamoxifen resistance and in the selection of optimized patient-tailored therapies.

The rs1800716 variant in CYP2D6 is associated with an increased double endometrial thickness in postmenopausal women on tamoxifen

BACKGROUND

Tamoxifen remains important in the treatment and prevention of estrogen receptor-positive breast cancer. In postmenopausal women, it can lead to endometrial changes such as cystic appearances, hyperplasia, polyps and endometrial cancer. Tamoxifen is metabolized by cytochrome P450 (CYP450) enzymes to the more active metabolite endoxifen. Several genetic variants in the CYP450 enzymes reduce tamoxifen metabolism, leading to reduced endoxifen levels. We hypothesize that carriers of these variants, which are established poor metabolizers of tamoxifen, do not have the typical tamoxifen-induced increase in endometrial thickness. We test the association between genetic variability in CYP450 enzymes and the increase in double endometrial thickness (DET) as measured through transvaginal ultrasound (TVU).

PATIENTS AND METHODS

We carried out a retrospective study on postmenopausal tamoxifen users for which germline DNA was available and at least one DET measurement was made between January 2000 and October 2011. Genotyping of 33 single nucleotide polymorphisms in CYP450 genes involved in tamoxifen metabolism was carried out using Sequenom MassARRAY. The association between these variants and TVU outcome (DET ≥5 mm) was assessed by proportional hazards regression.

RESULTS

Data were available for 184 women: 47 with a DET of <5 mm on all ultrasounds and 137 with a DET of ≥5 mm on at least one ultrasound. The rs1800716 variant in CYP2D6 showed a statistically significant association with DET. In particular, mutant carriers of rs1800716 had an increased chance of having a DET of ≥5 mm (P = 0.0022, false discovery rate 0.0179). None of the other variants were associated with DET.

CONCLUSION

Although mutant carriers of rs1800716 are characterized by reduced CYP2D6 enzyme activity and by low levels of endoxifen, we observed that mutant alleles of rs1800716 were associated with an increased chance of having a DET of ≥5 mm in postmenopausal women on tamoxifen. We conclude that the increase in endometrial thickness seen under tamoxifen cannot be used as a marker for favorable genotypes.

CLINICAL TRIAL NUMBER

B32220084284.