Effects of aromatase inhibitors and body mass index on steroid hormone levels in women with early and advanced breast cancer

BACKGROUND

Aromatase inhibitors (AIs) are central to the management of oestrogen receptor-positive breast cancer in the adjuvant and metastatic setting. Levels of circulating steroid hormones (SHs) were measured in patients established on AIs to investigate: the influence of body mass index (BMI) in both the adjuvant and metastatic setting; the class of AI utilized in the adjuvant setting (steroidal versus non-steroidal); and differences in SH levels between women treated adjuvantly and those receiving a second-line AI for locally advanced/metastatic disease.

METHODS

Plasma levels of androstenedione, 5-androstene-3β,17β-diol, dehydroepiandrosterone, oestradiol and testosterone were measured by radioimmunoassay in women with breast cancer who were receiving AIs in either an adjuvant or a metastatic setting. Differences between mean SH levels by class of AI, BMI, and second-line versus adjuvant therapy were assessed.

RESULTS

Sixty-four women were receiving AI therapy, 45 (70 per cent) in an adjuvant setting and 19 (30 per cent) were taking a second-line AI. There was no significant correlation between BMI and SH levels. However, BMI was significantly higher in the second-line AI cohort compared with the adjuvant cohort (29.8 versus 26.2 kg/m2 respectively; P = 0.026). In the adjuvant setting, patients receiving a steroidal AI had significantly higher levels of all five hormones (P < 0.050). In the second-line AI cohort, oestradiol levels were significantly higher than in the adjuvant cohort (4.5 versus 3.3 pg/ml respectively; P = 0.022). Multivariable analysis adjusted for BMI confirmed the higher residual oestradiol level in the second-line AI group (P = 0.063) and a significantly higher androstenedione level (P = 0.022).

CONCLUSION

Residual levels of SH were not significantly influenced by BMI. However, the significant differences in residual SH levels between the second-line and adjuvant AI cohort is of relevance in the context of resistance to AI therapy, and warrants further investigation.

The Role of the Androgen Receptor in Triple-Negative Breast Cancer

Greater than 70% of human breast cancers express the androgen receptor (AR). Emerging preclinical and clinical data suggest that AR may play a role in breast cancer pathogenesis and may serve as a therapeutic target in certain more difficult-to-treat breast cancer subtypes, such as triple-negative breast cancer. Although this is an area of active investigation, the clinical significance of this hormone receptor as a prognostic/predictive marker and its functional role in tumorigenesis is unclear. This review provides an update on the advances made in the last several years regarding the role of AR as a prognostic/predictive biomarker in breast cancer, the underlying biology of AR signaling in breast cancer development and the available clinical data for the use of androgen inhibition in the treatment of AR+ triple-negative breast cancer.

Endocrine therapy for advanced/metastatic breast cancer

First-line endocrine therapy by estrogen antagonism or suppression of estrogen achieves objective responses (ORs) and clinical benefit (CB) in around 30% and 50% of estrogen receptor-positive metastatic breast cancer patients, respectively. Aromatase inhibitors (AIs) are the most effective treatment in previously untreated postmenopausal women. Tamoxifen is an effective alternative. The optimal endocrine therapy on relapse remains uncertain. Tamoxifen and fulvestrant achieve CB in around 50% of patients and ORs of 10%. CB of exemestane after nonsteroidal AIs is 30% to 50% but ORs are rare. Targeted agents (eg, everolimus) plus endocrine therapy are likely to become increasingly important in overcoming endocrine resistance.

Emerging targeted agents in metastatic breast cancer

Extensive preclinical experimentation has conceptually changed the way we perceive breast cancer, with the wide spectrum of genomic alterations governing its malignant progression now being recognized. Functional genomics has helped us identify important genetic defects that can be pharmaceutically targeted in the setting of metastatic disease. Rationally chosen combination regimens are now under clinical investigation. Recent data underline the functional importance of the tumour-associated stroma, with several candidate molecular targets now emerging. Data elucidating a cellular hierarchy within the breast cancer cellular compartment support the existence of a therapy-resistant subpopulation of breast cancer stem cells. Identification of the developmental pathways that dictate their malignant phenotype and use of high-throughput screening techniques are leading to new therapeutic avenues. In this Review, we present the biological rationale for the clinical development of more than 15 different classes of targeted agents in breast cancer, along with evidence supporting rational combinations. However, metastatic breast cancer resembles a Darwinian evolutionary system, with 'driver' mutations and epigenetic changes determining clonal selection according to branching trajectories. This evolution is reflected in the molecular heterogeneity of the disease and poses severe impediments to the successful clinical development of emerging targeted agents.