Changes in bone mineral density during and after 3 years' use of tamoxifen or toremifene

To study the effects of tamoxifen and toremifene on bone mineral density (BMD) in postmenopausal women with breast cancer.

Seventy patients with stage II-III breast cancer were randomized to start either tamoxifen (n = 36; 20 mg per day) or toremifene (n = 34; 40 mg per day) for 3 years. BMD in the lumbar spine and in the proximal femur was measured by dual-energy X-ray absorptiometry both before and during the treatment and 1 year after the discontinuation of the anti-estrogens.

The baseline BMD measurements were comparable between the groups. In 3 years, lumbar BMD decreased by 1.7% in tamoxifen (P = 0.048) and 3.0% in toremifene (P = 0.001) users (ns between the groups), and femoral neck BMD by 0.9% (P = 0.040) and 1.3% (P = ns), respectively. The use of hormone replacement therapy (HRT) until the diagnosis of breast cancer was associated with decreases in lumbar BMD during anti-estrogen regimen (4% at 3 years) in contrast to unchanged lumbar BMD in women with no previous use of HRT. During the 1st year after the cessation of anti-estrogen, lumbar BMD did not change at all in either group whereas femoral BMD decreased in both the groups at the rate of 1.5-3.2%, as expected.

We conclude that tamoxifen (20 mg) and toremifene (40 mg) have similar bone-sparing efficacy that in lumbar spine extends up to 1 year after the cessation of these regimens. This effect is not seen in lumbar spine BMD in those postmenopausal women who discontinue HRT at the time of breast cancer diagnosis.