Long-term efficacy and safety of exemestane in the treatment of breast cancer

Bone Safety Profile of Steroidal Aromatase Inhibitor in Comparison to Non-Steroidal Aromatase Inhibitors in Post-Menopausal Women with Breast Cancer: A Network Meta-Analysis

Background and Objectives

Aromatase inhibitors (AIs) provide an alternative to tamoxifen as an adjuvant therapy for postmenopausal patients with breast cancer (BC). Large trials resulted better outcomes with AIs. Adjuvant therapy with AIs reduced the risk of relapse compared with tamoxifen. Systemic therapies for BC can interfere with bone turnover, either by affecting gonadal steroid hormone production or by inhibiting peripheral aromatization into estrogen. We aimed to evaluate the safety profile of bone-related events by comparing 3 AIs with tamoxifen and a placebo.

Methods

The Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines were used for network meta-analyses (NMAs). Searches were performed using PubMed, Embase/Medline, Cochrane, and Ovid databases. Randomized controlled trials comparing tamoxifen and placebo or other AIs to steroidal or nonsteroidal AIs in patients with BC reporting bone-related safety events were included in NMA. NMA in a Bayesian approach was performed using R software (ver 3.2), Gemtc package.

Results

Seventeen studies reporting 4 different bone-related endpoints were included. Although there was no statistical significance, treatment with exemestane lowered the incidence of bone pain (odds ratio [OR] vs. anastrozole and letrozole: 0.63, 0.54), fracture episodes (OR vs. anastrozole and letrozole: 0.84, 0.80), and osteoporosis (OR vs. anastrozole and letrozole: 0.85, 0.73) compared with letrozole and anastrozole. Reduction in bone mineral density was lesser in exemestane than in anastrozole (mean reduction in hip: 1.05; lumbar spine: 1.25). Treatment ranking with the surface under the cumulative ranking curve showed that exemestane was found to reduce the incidence of bone-related adverse events.

Conclusion

A lower incidence of bone-related safety events was observed in patients treated with exemestane.

Impact of nonsynonymous single nucleotide polymorphisms on in-vitro metabolism of exemestane by hepatic cytosolic reductases

OBJECTIVE

Exemestane (EXE) is a potent third-generation aromatase inhibitor used as endocrine therapy in breast cancer treatment and prevention. Characterization of its metabolic pathway is incomplete, with ambiguity existing in the identity of enzymes driving the production of its key metabolite, 17β-dihydroexemestane (17β-DHE). The impact of genetic variation on EXE metabolism is also unknown. This study aims to describe cytosolic reductase involvement in hepatic EXE metabolism and to assess the impact of functional polymorphisms on metabolite production.

MATERIALS AND METHODS

Phase I metabolites were identified in incubations of EXE with pooled human liver cytosol or recombinant protein for AKR1Cs and CBR1. Kinetic parameters characterizing EXE reduction were measured for purified wild-type enzymes, and nonsynonymous variants occurring at greater than 1% minor allele frequency using UPLC/MS/MS.

RESULTS

Human liver cytosol, CBR1, AKR1C1, AKR1C2, AKR1C3, and AKR1C4 reduce EXE to active primary metabolite 17β-DHE. The formation of a novel metabolite, 17α-DHE, was catalyzed by recombinant AKR1C4 and CBR1 in addition to hepatic cytosol. Variants AKR1C3 Arg258Cys and AKR1C4 Gly135Glu had significantly decreased affinity for EXE relative to their respective wild types. Five common AKR1C3 polymorphisms were associated with decreased rates of catalysis, whereas AKR1C4 Gly135Glu increased the velocity of EXE reduction.

CONCLUSION

AKR1Cs and CBR1 catalyze EXE reduction in vitro. These results imply that cytosolic ketosteroid reductases may participate in the EXE metabolic pathway in vivo. In addition, several common variants were associated with altered enzymatic activity, suggesting that functional polymorphisms could play an important role in overall EXE metabolism and activity by altering the extent and duration of 17β-DHE exposure.

Uptake of exemestane chemoprevention in postmenopausal women at increased risk for breast cancer

Despite their efficacy, uptake of selective estrogen receptor modulators for breast cancer chemoprevention remains low. Exemestane, an aromatase inhibitor, has recently been identified as a potential chemopreventive option with fewer serious side effects compared with selective estrogen receptor modulators in postmenopausal women. The purpose of this study was to assess the uptake of exemestane in a breast cancer prevention clinic. A retrospective chart review was conducted to capture chemoprevention uptake by postmenopausal women presenting to the Yale Breast Cancer Prevention Clinic between November 2011 and November 2012. Descriptive statistics of the study population have been presented. Statistical analyses were carried out using SAS 9.3 (SAS Institute Inc., Cary, North Carolina, USA) between December 2012 and February 2013. Of 90 postmenopausal women, 56 were eligible for chemoprevention. Their mean age was 56.8 years. Among the women, 39% had osteopenia or osteoporosis. Thirteen women chose to start chemoprevention medication (23%). Although 31% of the chemopreventive medication administered included exemestane, only four of 56 postmenopausal women opted for exemestane (7%). Chemoprevention uptake rates of postmenopausal women in the setting of a breast cancer prevention clinic are higher than that reported in the general population; however, they remain low overall despite the inclusion of exemestane as an option. A significant proportion of postmenopausal women have decreased bone density, which is a potential barrier to exemestane uptake. The results provide practical implications suggesting that exemestane may have limited impact on breast cancer chemoprevention uptake. Further investigations should focus on understanding the factors that influence, predict, and increase chemoprevention uptake.

A Rare Cause of Acute Kidney Injury in a Female Patient with Breast Cancer Presenting as Renal Colic

Renal infarction is a rare cause of acute kidney injury which could lead to permanent loss of renal function. A prompt diagnosis is necessary in order to achieve a successful revascularization of the occluded artery. Given the rarity of the disease and the paucity of the reported cases in the previous literature a high index of suspicion must be maintained not only in the classical cardiac sources of systemic emboli (atrial fibrillation, dilated cardiomyopathy, or endocarditis), but also in the situations when a hypercoagulable state is presumed. The unspecific presenting symptoms often mask the true etiology of the patient’s complaints. We present here a rare case of renal infarction that occurred in the setting of a hypercoagulable state, in a female patient with a history of breast cancer and documented hepatic metastases.