Evaluation of plasma and tissue estrogen suppression with third-generation aromatase inhibitors: of relevance to clinical understanding?

Superior suppression of serum estrogens during neoadjuvant breast cancer treatment with letrozole compared to exemestane

PURPOSE

The aromatase inhibitor letrozole and the aromatase inactivator exemestane are two of the most pivotal cancer drugs used for endocrine treatment of ER-positive breast cancer in all phases of the disease. Although both drugs inhibit CYP19 (aromatase) and have been used for decades, a direct head-to-head, intra-patient-cross-over comparison of their ability to decrease estrogen synthesis in vivo is still lacking.

METHODS

Postmenopausal breast cancer patients suitable for neoadjuvant endocrine therapy were randomized to receive either letrozole (2.5 mg o.d.) or exemestane (25 mg o.d.) for an initial treatment period, followed by a second treatment period on the alternative drug (intra-patient cross-over study design). Serum levels of estrone (E1), estradiol (E2), letrozole, exemestane, and 17-hydroxyexemestane were quantified simultaneously using a novel, ultrasensitive LC-MS/MS method established in our laboratory.

RESULTS

Complete sets of serum samples (baseline and during treatment with letrozole or exemestane) were available from 79 patients, including 40 patients starting with letrozole (cohort 1) and 39 with exemestane (cohort 2). Mean serum estrone and estradiol levels in cohort 1 were 174 pmol/L and 46.4 pmol/L at baseline, respectively. Treatment with letrozole suppressed serum E1 and E2 to a mean value of 0.2 pmol/L and 0.4 pmol/L (P < 0.001). After the cross-over to exemestane, mean serum levels of E1 and E2 increased to 1.4 pmol/L and 0.7 pmol/L, respectively. In cohort 2, baseline mean serum levels of E1 and E2 were 159 and 32.5 pmol/L, respectively. Treatment with exemestane decreased these values to 1.8 pmol/L for E1 and 0.6 pmol/L for E2 (P < 0.001). Following cross-over to letrozole, mean serum levels of E1 and E2 were significantly further reduced to 0.1 pmol/L and 0.4 pmol/L, respectively. Serum drug levels were monitored in all patients throughout the entire treatment and confirmed adherence to the protocol and drug concentrations within the therapeutic range for all patients. Additionally, Ki-67 values decreased significantly during treatment with both aromatase inhibitors, showing a trend toward a stronger suppression in obese women.

CONCLUSION

To the best of our knowledge, we present here for the first time a comprehensive and direct head-to-head, intra-patient-cross-over comparison of the aromatase inhibitor letrozole and the aromatase inactivator exemestane concerning their ability to suppress serum estrogen levels in vivo. All in all, our results clearly demonstrate that letrozole therapy results in a more profound suppression of serum E1 and E2 levels compared to exemestane.

Alternative dosing regimen of exemestane in a randomized presurgical trial: the role of obesity in biomarker modulation

In a 3-arm presurgical trial, four-six weeks exemestane 25 mg three times/week (TIW) was non-inferior to 25 mg/day (QD) in suppressing circulating estradiol in postmenopausal women with ER-positive breast cancer. Since obesity may decrease exemestane efficacy, we analyzed changes in sex steroids, adipokines, Ki-67, and drug levels in relation to obesity. Postmenopausal women with early-stage ER-positive breast cancer were randomized to either exemestane 25 mg QD (n = 57), 25 mg TIW (n = 57), or 25 mg/week (QW, n = 62) for 4-6 weeks before breast surgery. Serum and tissue pre- and post-treatment biomarkers were stratified by body mass index (BMI)< or ≥30 kg/m2. Post-treatment median exemestane and 17-OH exemestane levels were 5-6 times higher in the QD arm compared to the TIW arm. For obese women, TIW maintained comparable reductions to QD in systemic estradiol levels, although the reduction in estrone was less with the TIW regimen. There was less suppression of SHBG with the TIW versus the QD dose schedule in obese women which should result in less systemic bioavailable estrogens. Metabolically, the effect of the TIW regimen was similar to the QD regimen for obese women in terms of leptin suppression and increase in the adiponectin-leptin ratio. Reduction in tissue Ki-67 was less for obese women on the TIW regimen than QD, although changes were similar for non-obese women. Our findings suggest that TIW exemestane should be explored further for primary cancer prevention in both normal weight and obese cohorts.

Changes in serum estrogenic activity during neoadjuvant therapy with letrozole and exemestane

The aromatase inhibitors (AIs), letrozole (Femar®/Femara®) and exemestane (Aromasin®), are widely used to treat estrogen receptor (ER) positive breast cancer in postmenopausal patients. In the setting of metastatic breast cancer, these drugs may be used after another causing new responses in selected patients after progressing on the first choice. The precise explanation for this "lack of cross resistance" is still missing. NEOLETEXE is a neoadjuvant, randomized, open-label, cross-over trial. Postmenopausal patients with ER-positive, HER-2 negative, locally advanced breast cancer were enrolled. All patients were randomized to treatment starting with either letrozole or exemestane for at least 2 months followed by another 2 months on the alternative AI. The total estrogenic activities in blood samples were determined using the AroER tri-screen assay developed in the Chen laboratory. Using this highly sensitive assay, estrogenic activity was detected at three time points for all patients. Importantly, a significantly higher total estrogenic activity was found during therapy with exemestane compared to letrozole in 21 out of 26 patients. When letrozole was included in the AroER tri-screen assay, the estrogenic activities in most samples collected during exemestane treatment were further reduced, suggesting that low levels of androgens remained in specimens obtained after exemestane treatment. Our results suggest the AroER tri-screen to be a very sensitive method to estimate the overall estrogen-mediated activity in human samples even during therapy with highly potent aromatase inhibitors. In the present study, serum estrogen activity was significantly higher during exemestane therapy when compared to letrozole therapy.

Tumour-infiltrating lymphocytes and response to neoadjuvant letrozole in patients with early oestrogen receptor-positive breast cancer: analysis from a nationwide phase II DBCG trial

Background

The presence of tumour-infiltrating lymphocytes (TILs) is associated with response to neoadjuvant chemotherapy among patients with triple-negative and HER2-positive breast cancer. However, the significance of TILs is less clear in luminal breast cancer. Here, we in postmenopausal patients with primary oestrogen receptor-positive (ER+), HER2 normal, operable breast cancer assessed the importance of inducing TILs during 4 months of letrozole on response in a neoadjuvant phase II study.

Methods

Participants were postmenopausal women with ER+, HER2 normal operable breast cancer assigned to 4 months of neoadjuvant letrozole. Pretreatment core biopsies and surgical specimens were assessed centrally for the percentage of TILs on haematoxylin and eosin-stained slides according to the International Immuno-Oncology Biomarker Working Group on Breast Cancer guidelines. Pathological response was assessed by the Residual Cancer Burden (RCB) index and a modified Miller-Payne grading system and was analysed according to change in TILs.

Results

Tumour specimens were available from 106 of the 112 patients treated per protocol. TIL concentration increased with mean 6.8 percentage point (p < 0.0001) during treatment (range − 39 to 60). An increase in TILs was significantly associated with pathological response with OR = 0.71 (95% CI 0.53–0.96; p = 0.02) per 10% absolute increase for pathological response and correspondingly OR = 0.56 (95% CI 0.40–0.78; p = 0.0007) for lower RCB index per 10% increase.

Conclusion

Increasing TILs during letrozole was significantly associated with a poor treatment response. An increase in TILs during endocrine therapy might imply immunogenicity, and these patients could be targetable by immunotherapy.

Trial registration

ClinicalTrials.govNCT00908531, registered 27 May 2009.

Clinical utility of exemestane in the treatment of breast cancer

Breast cancer is the most prevalent cancer in women, causing a significant mortality worldwide. Different endocrine strategies are available for the treatment of hormone-sensitive breast cancer, including antiestrogen tamoxifen and fulvestrant, as well as third-generation aromatase inhibitors (AIs), such as letrozole, anastrozole, and exemestane. In this review, we will focus on exemestane, its clinical use, and its side effects. Exemestane is a steroidal third-generation AI now used in all treatment settings for breast cancer. In the metastatic disease, it has been extensively investigated as the first-, second-, and further-line treatment and it is now registered for the treatment of postmenopausal women with advanced estrogen-receptor-positive breast cancer whose disease has progressed following antiestrogen therapy. A potential lack of cross-resistance with nonsteroidal AIs has been described, giving additional therapeutic opportunities in sequences of endocrine agents. Exemestane is also approved for the adjuvant treatment of postmenopausal early breast cancer, either as upfront monotherapy for 5 years, as a switch following 2–3 years of tamoxifen, or as extended therapy beyond 5 years of adjuvant treatment. New promising data also showed a beneficial effect in young premenopausal early breast cancer patients, when administered together with ovarian suppression. Interesting results have also emerged when exemestane has been investigated as neodjuvant treatment as well as preventive agent in healthy women at high risk for breast cancer. Exemestane is generally well tolerated, with a side effect profile similar to that of other AIs, including menopausal symptoms, arthralgia, and bone loss. In conclusion, exemestane can be considered an effective and well-tolerated endocrine treatment option for all stages of breast cancer.

Aromatase inhibitors in the breast cancer clinic: focus on exemestane

Breast cancer is the most prevalent type of cancer in women and responsible for significant female cancer-related mortality worldwide. In the Western world, over 80% of breast cancers are hormone-receptor positive for which endocrine therapy is administered. The main anti-estrogen treatments in use consist of selective estrogen-receptor modulators, such as tamoxifen, and third-generation aromatase inhibitors (AIs), such as exemestane, letrozole, and anastrozole. In this review, the focus will lie on exemestane, its clinical use, and its side-effect profile. Exemestane is the only third-generation steroidal AI. Its efficacy as a first-line treatment in metastatic breast cancer has been demonstrated. Therefore, exemestane could be considered a valid first-line therapeutic option, but it also can be used in second-line or further situations. Exemestane is mostly used as part of sequential adjuvant treatment following tamoxifen, but in this setting it is also active in monotherapy. Furthermore, this AI has been studied in the neoadjuvant setting as presurgical treatment, and even as chemoprevention in high-risk healthy postmenopausal women. It may reverse side effects of tamoxifen, such as endometrial changes and thromboembolic disease but may also cause some inconvenient side effects itself. Additionally, there is a lack of total cross-resistance between exemestane and nonsteroidal AIs as far as their anti-tumoral efficacy is concerned; moreover the two classes of AIs display a nontotal overlapping toxicity profile. Taking together, exemestane can be considered as a useful treatment option at all stages of breast cancer.

Analysis of estrogens in serum and plasma from postmenopausal women: past present, and future

Previous studies have shown that the selection of women who are at high breast cancer risk for treatment with chemoprevention agents leads to an enhanced benefit/risk ratio. However, further efforts to implement this strategy will require the development of new models to predict the breast cancer risk of particular individuals. Postmenopausal women with elevated plasma or serum estrogens are at increased risk for breast cancer. Therefore, the roles of various enzymes involved in the biosynthesis of estrogens in postmenopausal women have been reviewed in detail. In addition, the potential genotoxic and/or proliferative effects of the different estrogen metabolites as risk factors in the etiology of breast cancer have been examined. Unfortunately, much of the current bioanalytical methodology employed for the analysis of plasma and serum estrogens has proved to be problematic. Major advances in risk assessment would be possible if reliable methodology were available to quantify estradiol and its major metabolites in the plasma or serum of postmenopausal women. High performance liquid chromatography (HPLC) coupled with radioimmunoassay (RIA) currently provides the most sensitive and best validated immunoassay method for the analysis of estrone and estradiol in serum samples from postmenopausal women. However, inter-individual differences in specificity observed with many other immunoassays have caused significant problems when interpreting epidemiologic studies of breast cancer. It is almost impossible to overcome the inherent assay problems involved in using RIA-based methodology, particularly for multiple estrogens. For reliable measurements of multiple estrogens in plasma or serum, it will be necessary to employ stable isotope dilution methodology in combination with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Extremely high sensitivity can be obtained with pre-ionized estrogen derivatives when employed in combination with a modern triple quadrupole mass spectrometer and nanoflow LC. Using [(13)C(6)]-estrone as the internal standard it has proved possible to analyze estrone as its pre-ionized Girard T (GT) derivative in sub-fg (low amol) amounts on column. This suggests that in the future it will be possible to routinely conduct LC-MS assays of multiple estrogen metabolites in serum and plasma at even lower concentrations than the current lower limit of quantitation of 0.4pg/mL (1.6pmol/L). The ease with which the pre-ionization derivatization strategy can be implemented will make it possible to readily introduce high sensitivity stable isotope dilution methodology in laboratories that are currently employing LC-MS/MS methodology. This will help conserve important plasma and serum samples as it will be possible to conduct high sensitivity analyses using low sample volumes.