Changes in bone turnover and in bone mass in women with breast cancer switched from tamoxifen to exemestane

Recently the third generation aromatase inhibitors have proved their efficacy and tolerability compared with tamoxifen in the adjuvant treatment of women with hormone responsive early breast cancer. However, there is some concern about the possible negative impact of these drugs on bone. The aim of the study was to evaluate the effects of the steroidal aromatase inactivator exemestane on bone turnover markers and on bone mineral density (BMD). Seventy postmenopausal women (62.0±8.9 years) with completely resected breast cancer and who were disease-free following 2–3 years on tamoxifen were randomly assigned to continue tamoxifen (n=36) or switch to exemestane (n=34). Sixty-one patients completed the 2-year study period. Bone alkaline phosphatase (B-ALP) and the carboxy-terminal telopeptide of type I collagen (CTX) were measured at baseline and after 3, 6, 9, 12, 18 and 24 months. BMD at lumbar spine (BMD-LS), at femoral neck (BMD-FN), at total hip (BMD-T) and at whole body (BMD-WB) were measured at 6-monthly intervals. Exemestane-treated women showed significant (p<0.01) increases with respect to baseline in both B-ALP and CTX. The difference between the 2 groups reached the statistical significance at month 6 for CTX (p<0.05) and at month 9 for B-ALP (p<0.01). Moreover, the exemestanetreated women showed an early decrease in PTH serum levels (−20.4%, p<0.01 at month 6). In the E group, the percentage changes were −2.37 (p<0.05) BMD-LS, −1.24 (p<0.05) BMD-FN, −1.1 (n.s.) BMD-T, −1.03 (n.s.) BMD-WB at month 12 and −2.99 (p<0.01) BMD-LS, −1.92 (p<0.01) BMD-FN, −2.01 (p<0.05) BMD-T, −1.3 (n.s.) BMD-WB at month 24. The tamoxifen group did not show significant changes in BMD. The differences between the two groups were significant at all skeletal sites except BMD-WB. Our data suggest that switching postmenopausal women from tamoxifen to exemestane causes a marked increase in bone turnover markers with a consequent reduction in BMD. These findings could be due to both the direct effect of exemestane and to the loss of the protective effect of tamoxifen. Therefore, the postmenopausal women switched from tamoxifen to exemestane should be monitored for bone loss especially if other risk factors for osteoporosis are present.