Long-term “protective” effect of aromatase inhibitors on the endometrium of postmenopausal breast cancer patients

Dysregulation of Aromatase in Breast, Endometrial, and Ovarian Cancers: An Overview of Therapeutic Strategies

Aromatase is the rate-limiting enzyme in the biosynthesis of estrogens, which play crucial roles on a spectrum of developmental and physiological processes. The biological actions of estrogens are classically mediated by binding to two estrogen receptors (ERs), ERα and ERβ. Encoded by the cytochrome P450, family 19, subfamily A, polypeptide 1 (CYP19A1) gene, aromatase is expressed in a wide variety of tissues, as well as benign and malignant tumors, and is regulated in a pathway- and tissue-specific manner. Overexpression of aromatase, leading to elevated systemic levels of estrogen, is unequivocally linked to the pathogenesis and growth of a number malignancies, including breast, endometrium, and ovarian cancers. Aromatase inhibitors (AIs) are routinely used to treat estrogen-dependent breast cancers in postmenopausal women; however, their roles in endometrial and ovarian cancers remain obscure. While AI therapy is effective in hormone sensitive cancers, they diminish estrogen production throughout the body and, thus, generate undesirable side effects. Despite the effectiveness of AI therapy, resistance to endocrine therapy remains a major concern and is the leading cause of cancer death. Considerable advances, toward mitigating these issues, have evolved in conjunction with a number of histone deacetylase (HDAC) inhibitors for countering an assortment of diseases and cancers, including the aforesaid malignancies. HDACs are a family of enzymes that are frequently dysregulated in human tumors. This chapter will discuss the current understanding of aberrant regulation and expression of aromatase in breast, endometrial, and ovarian cancers, and potential therapeutic strategies for prevention and treatment of these life-threatening diseases.

Endometrial cancer risk in postmenopausal breast cancer patients treated with tamoxifen or aromatase inhibitors

INTRODUCTION

The gynaecological toxicity profile of tamoxifen presents a significant burden to the patients and oncologist as tamoxifen-related side effects result in additional investigations, procedures and referrals. Aromatase inhibitor have been shown to result in significant reduction in gynaecological problems, possibly including endometrial cancer. Areas covered: We reviewed the main breast cancer trials, observation or cohort studies investigating tamoxifen or an aromatase inhibitor to report on endometrial adverse events and cancer. Expert commentary: Evidence for an increase in endometrial cancers with tamoxifen in breast cancer treated patients is now very clear. Aromatase inhibitors have shown to have a beneficial effect on the endometrium. There is an important need for further studies to clearly determine the influence of aromatase inhibitors on the endometrial in tamoxifen-naïve women. The effect of aromatase inhibitors on gynaecological problems may have potentially a very important impact in clinical practice.

Aromatase inhibitors, tamoxifen, and endometrial cancer in breast cancer survivors

BACKGROUND

The risks of both endometrial cancer and postmenopausal breast cancer are increased by obesity and higher endogenous estrogen levels. Although aromatase inhibitors reduce breast cancer incidence, their influence on endometrial cancer is uncertain.

METHODS

The authors investigated this issue in a cohort of 17,064 women who were diagnosed with hormone receptor-positive breast cancer in an integrated group practice health plan. Information on demographics, comorbidities, and the receipt of adjuvant endocrine therapy was available from electronic medical records and pharmacy records, respectively. Endometrial cancer information was obtained from the health plan's Surveillance, Epidemiology, and End Results-affiliated tumor registry, and rates were compared across endocrine therapy groups (aromatase inhibitor, n = 5303; tamoxifen, n = 5155; switchers: both [n = 3787] or none [n = 2819]) using multivariable adjusted Cox proportional-hazards models.

RESULTS

Endometrial cancer incidence was a statistically significant 48% lower in the aromatase inhibitor group versus the tamoxifen group (hazard ratio, 0.52; 95% confidence interval, 0.31-0.87; P = .01). Endometrial cancer incidence was 29% lower in the aromatase inhibitor group versus the no endocrine therapy group (hazard ratio, 0.71; 95% confidence interval, 0.37-1.35; P = .30) and 33% lower in the aromatase inhibitor group versus the tamoxifen group (hazard ratio, 0.67; 95% confidence interval, 0.42-1.06; P = .08), but neither difference was statistically significant. Associations were stronger among those with good drug adherence.

CONCLUSIONS

In a community-based, integrated health plan setting, endometrial cancer incidence was lower in women who were receiving an aromatase inhibitor compared with those who were receiving tamoxifen. In addition, aromatase inhibitors may mitigate the incidence of tamoxifen-associated endometrial cancer. Although there were somewhat fewer endometrial cancers in the aromatase inhibitor group versus the no endocrine therapy group, further studies are needed for the definitive assessment of this potential association.

Microwave endometrial ablation for endometrial protection in women with breast cancer on adjuvant tamoxifen

AIM

The purpose of the current study was to determine the effectiveness of microwave endometrial ablation (MEA) in inhibiting the proliferative response of the endometrium in women with breast cancer who are treated with tamoxifen.

MATERIAL AND METHODS

In the before-after study, we treated 31 postmenopausal patients who had received adjuvant tamoxifen for 1 year or more with MEA, the endometrial changes were compared before and after MEA.

RESULTS

After MEA, the thickness of the uterine lining was decreased significantly. No patient had recurrent endometrial polyps or abnormal vaginal bleeding during the follow-up period.

CONCLUSION

MEA had a protective action against the uterine effects of tamoxifen for postmenopausal patients. MEA is a safe and effective minimally invasive treatment method for breast cancer patients treated with tamoxifen.

Expression of estrogen receptors (α, β), cyclooxygenase-2 and aromatase in normal endometrium and endometrioid cancer of uterus

PURPOSE

Endometrial cancer (EC) is one of the most common malignancies of the female genital tract, but the etiology, especially its metabolism is still investigated. The aim of this study was to evaluate the presence and relative expression of Estrogen Receptors (α, β), Cyclooxygenase-2 and Aromatase in both endometrial cancer and normal mucosa.

MATERIAL/METHODS

Two groups of women were selected for the study: 1) patients with endometrioid endometrial cancer (FIGO I; G1 - G3) (n=35) and 2) subjects with normal endometrial tissue (control group, n=29). The expression of Estrogen Receptors (ERα, β), Cyclooxygenase-2 (COX-2), Aromatase were estimated by Western blot analysis. Furthermore, the associations between FIGO classification (stage: Ia, Ib), tumor grade (G) and expression of ERα, β, COX-2, aromatase proteins were evaluated. Overall and disease-free survival curves were generated according to the Kaplan-Meier method. Median follow-up time of the patients examined in this study was 39 months.

RESULTS

The relative expression of each examined protein was markedly higher in the endometrial cancer tissue as compared to the healthy endometrium. The trends towards greater expression along with a tumor progression was noticed (FIGO stage: Ia vs. Ib). Analysis of endometrial cancer risk factors and their influence on survival curves showed only an inverse significant correlations between obesity (BMI: 36.2; n=21) and disease-free survival in EC group (p=0.00872), but there was no significant association between obesity and overall survival (p=0.358).

CONCLUSIONS

Endometrioid endometrial cancer shows relatively higher expression of either ER, COX-2 and aromatase comparing to healthy mucosa, suggesting their involvement in tumor development and progression.

The ATAC adjuvant breast-cancer trial: six-year results of the endometrial subprotocol

Postmenopausal women with localised, early breast cancer (n = 285) were enrolled in a prospective subprotocol of the 'arimidex, tamoxifen, alone or in combination' (ATAC) trial to assess gynaecological abnormalities arising during treatment with anastrozole (1 mg/day) or tamoxifen (20 mg/day). After 6 years' follow-up, there appeared to be non-significantly fewer endometrial abnormalities with anastrozole than with tamoxifen (12.4% vs 20.2%, odds ratio 0.52; 95% confidence intervals 0.20, 1.32; p = 0.17). The time to first endometrial abnormality was non-significantly longer for patients receiving anastrozole compared with tamoxifen (hazard ratio 0.57; 95% confidence intervals 0.26, 1.22; p = 0.15), with most abnormalities occurring within the first year of treatment. Fewer patients treated with anastrozole appeared to require medical intervention for endometrial abnormalities, compared with patients on tamoxifen. This study showed that there was no significant difference in endometrial pathology between anastrozole and tamoxifen treatment groups.