Adjuvant trials of aromatase inhibitors: determining the future landscape of adjuvant endocrine therapy

Effect of an aromatase inhibitor on bmd and bone turnover markers: 2-year results of the Anastrozole, Tamoxifen, Alone or in Combination (ATAC) trial (18233230)

Aromatase inhibitors reduce estrogen levels in postmenopausal women with breast cancer. Residual estrogen is an important determinant of bone turnover. Adjuvant anastrozole was associated with significant BMD loss and increased bone remodeling, whereas tamoxifen reduced bone marker levels.

INTRODUCTION

In the Anastrozole, Tamoxifen, Alone or in Combination (ATAC) trial after a median follow-up of 68 months, a significant improvement in disease-free survival was observed with anastrozole treatment (hazard ratio [HR], 0.87; 95% CI, 0.78-0.97; p = 0.01). Anastrozole was also associated with tolerability benefits compared with tamoxifen, but with higher fracture rates. The HR of anastrozole compared with tamoxifen after 60 months of treatment was 1.49 (95% CI, 1.25-1.77).

MATERIALS AND METHODS

This prospectively designed subprotocol (n = 308) of ATAC assessed changes in BMD and bone turnover markers in postmenopausal women with invasive primary breast cancer receiving anastrozole 1 mg/day, tamoxifen 20 mg/day, or combination treatment with both agents for 5 years. Patients with osteoporosis were excluded (osteopenia permitted at the investigators discretion). Lumbar spine and total hip BMD was assessed at baseline and after 1 and 2 years; bone turnover markers (serum C-telopeptide, urinary N-telopeptide [NTX], free deoxypyridinoline, serum procollagen type-1 N-propeptide, bone alkaline phosphatase [ALP]) were assessed at baseline and after 3, 6, and 12 months. Results were expressed as median percentage change.

RESULTS

After 2 years of anastrozole treatment, BMD was lost at lumbar spine (median 4.1% loss) and total hip (median 3.9% loss) sites; increases of 2.2% and 1.2%, respectively, were observed with tamoxifen. After 1 year of anastrozole treatment, increased bone remodeling was observed (NTX, +15%; 95% CI, 3-25%; bone ALP, +20%; 95% CI, 14-25%); decreased bone remodeling was observed with tamoxifen (NTX, -52%; 95% CI, -62% to -33%; bone ALP, -16%; 95% CI, -24% to -11%).

CONCLUSIONS

Anastrozole is associated with significant BMD loss and a small increase in bone turnover, whereas tamoxifen (and the combination) is associated with increased BMD and decreased remodeling. These data may explain the increased fracture risk observed with anastrozole treatment in the ATAC trial. The impact of anastrozole on bone should be weighed against its overall superior efficacy and tolerability as observed in the main ATAC trial.

Chlorambucil and lomustine (CL56) in absolute hormone refractory prostate cancer: re-induction of endocrine sensitivity an unexpected finding

The management of androgen independent prostate cancer is increasingly disputed. Diethylstilbestrol and steroids have useful second-line activity in its management. The value of chemotherapy still remains contentious. This paper reports a phase 2 study of two orally active chemotherapy drugs in patients who are absolutely hormone refractory having failed primary androgen blockade and combined oestrogens and corticosteroids. In total, 37 patients who were biochemically castrate with absolute hormone refractory prostate cancer and performance status of 0–3 were enrolled. Therapy consisted of chlorambucil 1 mg kg⁻¹ given as 6 mg a day until the total dose was reached and lomustine 2 mg kg⁻¹ given every 56 days (CL56). During this time all hormone therapy was stopped. One patient normalised his PSA with a further two having a greater than 50% decline leading to an objective response rate of 10%. The median time to progression was 3.6 months with an overall survival of 7.1 months. The median survival of this group of patients from first becoming androgen independent was 23.5 months. Eight of 17 (47%) patients who were subsequently re-challenged with hormonal therapy following failure of chemotherapy had a further PSA reduction, three (17%) of which were >50%. The median progression-free interval for the eight patients was 4 months. In conclusion, CL56 has a low objective response rate in the management of absolute hormone refractory prostate cancer. Toxicity was mild. Re-induction of hormone sensitivity following failure of chemotherapy was an unexpected finding that requires further study.

Emerging role of aromatase inhibitors in the adjuvant setting

Aromatase inhibitors (AIs) have been approved as second-line treatment for estrogen receptor-positive (ER+) metastatic breast cancer after first-line treatment with the selective estrogen receptor modulator (SERM) tamoxifen. Anastrozole and letrozole have also recently been widely approved as first-line endocrine therapy for postmenopausal women with hormone receptor-positive metastatic breast cancer. The three third-generation selective oral AIs approved for use in the United States include two nonsteroidal agents, anastrozole (Arimidex) and letrozole (Femara), and the irreversible steroidal inhibitor exemestane (Aromasin). Several major ongoing clinical trials with a variety of treatment regimens are comparing the relative efficacy of tamoxifen with the steroidal and nonsteroidal AIs in the adjuvant setting. The first strategy compares an AI against tamoxifen directly. Among these are the ATAC (Arimidex, Tamoxifen Alone or in Combination) trial (anastrozole), the BIG FEMTA (Femara-Tamoxifen Breast International Group) trial (letrozole), and the EXEM and TEAM (exemestane) trials. A second strategy is examining the use of an AI as an extension after the initial 5 years of tamoxifen. Examples of this trial design are the MA-17 (letrozole) and the National Surgical Adjuvant Breast and Bowel Project (NSABP B-33, exemestane) trials. A third approach is the use of these agents in sequence with tamoxifen as therapy within the initial 5 postoperative years. Examples of this approach are the International Collaboration Cancer Group trial (tamoxifen for 2-3 years followed by either tamoxifen or exemestane for the remainder of the 5-year period), the BIG FEMTA trial (patients are crossed over from tamoxifen to Ietrozole or letrozole to tamoxifen), and the Arimidex-Nolvadex (ARNO) trial (patients receiving tamoxifen are randomized either to continue with tamoxifen or to switch to anastrozole). A single trial is comparing tamoxifen and anastrozole as initial 5-year therapy, or a combination of the two. The study addressing this design is the ATAC trial. Finally, a small trial in Norway is comparing 2 years of an AI versus a placebo in very low-risk patients with receptor-positive breast tumors. Most adjuvant trials have companion studies associated with the main protocol. These are to determine the end-organ effects of the inhibitors and include measurements of quality of life, bone and lipid metabolism, and endometrial effects. This review addresses the clinical implications of these studies of AIs.

Effects of anastrozole on lipid metabolism compared with tamoxifen in rats

BACKGROUND

Anastrozole, a new aromatase inhibitor, has been used to treat postmenopausal metastatic breast cancer, and several clinical trials of adjuvant treatment using this agent are ongoing. However, the effects of anastrozole on lipid metabolism are unknown. The aim of this study was to evaluate the effect of anastrozole on lipid metabolism, especially lipoprotein lipase (LPL) activity, compared with tamoxifen in rats.

METHODS

Ovariectomized female rats were divided into six groups: C, controls; T, tamoxifen treatment; A, anastrozole treatment; CAT, combined anastrozole/tamoxifen treatment; NAT, no treatment after tamoxifen; and AAT, anastrozole treatment after tamoxifen. The agents were orally administered for 3 weeks. Serum total cholesterol, triglycerides, and LPL activity in postheparin plasma were measured at the end of the experiment.

RESULTS

Serum cholesterol levels were significantly lower in the T and CAT groups than in controls (P < 0.001). Serum triglyceride levels were significantly higher in the T group than in the other groups (P < 0.001). LPL activity was significantly lower in T and AAT groups (P < 0.01). There was no significant difference in any parameters in group A.

CONCLUSIONS

Anastrozole does not affect lipid metabolism including LPL activity. There was little effect on lipid profiles during combination treatment or following treatment with tamoxifen. In a clinical setting, therefore, anastrozole might be safe for patients with abnormal triglyceride profiles during tamoxifen treatment.