Update on aromatase inhibitors in breast cancer

Chemoresistance and targeted therapies in ovarian and endometrial cancers

Gynecological cancers are known for being very aggressive at their advanced stages. Indeed, the survival rate of both ovarian and endometrial cancers is very low when diagnosed lately and the success rate of current chemotherapy regimens is not very efficient. One of the main reasons for this low success rate is the acquired chemoresistance of these cancers during their progression. The mechanisms responsible for this acquired chemoresistance are numerous, including efflux pumps, repair mechanisms, survival pathways (PI3K/AKT, MAPK, EGFR, mTOR, estrogen signaling) and tumor suppressors (P53 and Par-4). To overcome these resistances, a new type of therapy has emerged named targeted therapy. The principle of targeted therapy is simple, taking advantage of changes acquired in malignant cancer cells (receptors, proteins, mechanisms) by using compounds specifically targeting these, thus limiting their action on healthy cells. Targeted therapies are emerging and many clinical trials targeting these pathways, frequently involved in chemoresistance, have been tested on gynecological cancers. Despite some targets being less efficient than expected as mono-therapies, the combination of compounds seems to be the promising avenue. For instance, we demonstrate using ChIP-seq analysis that estrogen downregulate tumor suppressor Par-4 in hormone-dependent cells by directly binding to its DNA regulatory elements and inhibiting estrogen signaling could reinstate Par-4 apoptosis-inducing abilities. This review will focus on the chemoresistance mechanisms and the clinical trials of targeted therapies associated with these, specifically for endometrial and ovarian cancers.

Use of aromatase inhibitors as first- and second-line medical therapy in patients with endometrial adenocarcinoma: a retrospective study

OBJECTIVES

The primary objective of this study was to examine the role of aromatase inhibitors (AIs) as first- or second-line medical treatment in women with endometrial adenocarcinoma who were not candidates for surgical management. The secondary objective was to examine the role of AIs in adjuvant and palliative treatment.

METHODS

Thirty women with endometrial adenocarcinoma who were treated with aromatase inhibitors between 2000 and 2010 at the Tom Baker Cancer Centre in Calgary, Alberta were assessed in a retrospective analysis. Disease response was based on response evaluation criteria in solid tumours. Kruskal-Wallis test was used to compare non-parametric variables and Fisher exact test was used to compare the health variables.

RESULTS

Seventeen patients received AIs as first- or second-line medical treatment, five received adjuvant therapy, and eight received palliative treatment. The median age of patients in the first or second line medical treatment group was significantly greater than that of patients in the adjuvant or palliative group (P = 0.042). There was no significant difference in median weight or body mass index. The subjective clinical response rate with medical treatment was 70%. In the first- or second-line medical treatment group, only seven patients had available response data. Our study showed stable disease in 5/7 (71%), partial response in 1/7 (14%), and progression in 1/7 (14%) patients.

CONCLUSION

This retrospective clinical series examining use of an aromatase inhibitor as first- or second-line medical therapy in women with endometrial carcinoma showed that AIs are a potential treatment for patients who have a contraindication to surgery and who either have failed or cannot use megestrol therapy.

Uterine Sarcoma and Aromatase Inhibitors: Tom Baker Cancer Centre Experience and Review of the Literature

Objectives

Uterine sarcomas are a rare group of mesenchymal tumors with a poor prognosis and aggressive biology. Standard treatment involves surgical staging. The role of further adjuvant treatment is unclear. The goals of this study were to determine the response rates to treatment of patients with uterine sarcomas and to review the currently available literature on the use of aromatase inhibitors (AIs).

Materials and Methods

We performed a retrospective analysis on all patients with uterine sarcoma treated with an AI between 2000 and 2010 at the Tom Baker Cancer Centre in Calgary, Alberta.

Results

Four patients with endometrial stromal sarcoma and 3 patients with leiomyosarcoma received treatment with an AI. A literature search resulted in 10 case reports and 4 retrospective studies of patients with endometrial stromal sarcoma and 1 case report and 2 retrospective studies of patients with leiomyosarcoma. On the basis of the available literature, combined with the current findings, the overall response rate of endometrial stromal sarcoma to AIs is 67% (complete response of 7% and partial response of 60%), and the partial response rate of leiomyosarcoma to AIs is 11%, with no reported complete responses.

Conclusions

Aromatase inhibitors are a well-tolerated class of medications that are effective in the treatment of endometrial stromal sarcomas. These medications may also have a role to help stabilize disease progression in the treatment of leiomyosarcoma. More large, prospective, multicentered trials will be needed to clarify this issue.

Exemestane: a review of its use in postmenopausal women with breast cancer

Exemestane (Aromasin) is an orally active steroidal irreversible inactivator of the aromatase enzyme indicated as an adjuvant treatment in postmenopausal women with estrogen receptor-positive early-stage breast cancer following 2-3 years of adjuvant treatment with tamoxifen, and for the treatment of advanced breast cancer in postmenopausal women whose disease has progressed following tamoxifen or other antiestrogen therapy. Exemestane is effective for the treatment of postmenopausal women with early-stage or advanced breast cancer. In early-stage disease, switching to exemestane for 2-3 years after 2-3 years of adjuvant tamoxifen treatment was more effective in prolonging disease-free survival than continuing tamoxifen therapy, although it was not associated with an overall survival benefit, except in those with estrogen receptor-positive or unknown receptor status disease when nodal status, hormone replacement therapy (HRT) and chemotherapy use were adjusted for. Moreover, preliminary data suggest that the efficacy of exemestane is generally no different to that of tamoxifen in the primary adjuvant treatment of early-stage breast cancer, although exemestane may be better in prolonging the time to distant recurrence. In advanced disease, exemestane showed equivalent efficacy to megestrol in patients with disease refractory to tamoxifen and an efficacy not significantly different from that of fulvestrant in those refractory to a nonsteroidal aromatase inhibitor. Available data, some of which are limited, suggest exemestane is also effective in the first-line hormonal treatment of advanced breast cancer in postmenopausal women. Exemestane is generally well tolerated, although the potential bone fracture risk of the drug requires further investigation. Results from directly comparative trials indicating the efficacy, tolerability and bone fracture risk of exemestane relative to third-generation aromatase inhibitors and other agents in both early-stage and advanced disease, as well as the optimal sequence of endocrine therapies, are awaited with interest. In the meantime, switching to exemestane should be considered in postmenopausal women who have received 2-3 years of adjuvant tamoxifen treatment for early-stage breast cancer, and is an emerging treatment option for postmenopausal women with advanced breast cancer refractory to one or more antiestrogen therapies.

Aromatase expression predicts survival in women with early-stage non small cell lung cancer

Estrogen signaling is critical in the progression of tumors that bear estrogen receptors. In most patients with breast cancer, inhibitors that block interactions of estrogen with its receptors or suppress the production of endogenous estrogens are important interventions in the clinic. Recent evidence now suggests that estrogen also contributes to the pathogenesis of non-small cell lung cancer (NSCLC). We used a human lung cancer xenograph model system to analyze the effect of aromatase or estradiol on tumor growth. We further examined the level of protein expression of aromatase in 422 patients with NSCLC using a high-density tissue microarray. Results were confirmed and validated on an independent patient cohort (n = 337). Lower levels of aromatase predicted a greater chance of survival in women 65 years and older. Within this population, the prognostic value of aromatase was greatest in earlier stage lung cancer (stage I/II). In addition, for women with no history of smoking, lower aromatase levels were a strong predictor of survival. Our findings implicate aromatase as an early-stage predictor of survival in some women with NSCLC. We predict that women whose lung cancers have higher levels of aromatase might be good candidates for targeted treatment with aromatase inhibitors.

Hormonal therapies and gynaecological cancers

Hormonal therapy has an established place in the management of women with gynaecological malignancies, including first-line therapy for recurrent receptor-positive endometrial cancer and low-grade stromal sarcoma. There is no place for adjuvant hormonal treatment of these cancers after primary surgery. Primary treatment with either oral or intra-uterine progestagens to preserve fertility in younger women with endometrial carcinoma is effective in about 70% of cases. Response rates to tamoxifen in advanced/recurrent ovarian cancers approximates 10%. To the authors' knowledge, no studies that reasonably compare different progestagens, different routes of therapy, different doses and different hormonal preparations have been published.