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Division of Hematology and Oncology (M.R.S., M.A.F.) and Endocrine Unit (J.S.F.), Department of Medicine, and the Biostatistics Center (H.L.), Massachusetts General Hospital, Boston, Massachusetts 02114
Address all correspondence and requests for reprints to: Dr. Matthew R. Smith, Massachusetts General Hospital, Cox 640, 100 Blossom Street, Boston, Massachusetts 02114. E-mail: smith.matthew{at}mgh.harvard.edu.
| Abstract |
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| Introduction |
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Osteoporosis is an important complication of GnRH agonist treatment in men with prostate cancer. GnRH agonists decrease bone mineral density (1, 2, 3, 4) and increase fracture risk (5, 6, 7, 8).
Estrogens play an important role in skeletal homeostasis in normal men. Estrogen receptors are expressed in osteoblasts and osteoclasts (9, 10, 11). In older men, serum estradiol levels are positively associated with spinal bone mineral density and negatively associated with vertebral fracture risk (12, 13, 14). Estrogens contribute to the regulation of both bone formation and bone resorption in men (15, 16).
Raloxifene is a selective estrogen receptor modulator that mimics the effects of estrogens in bone without stimulatory effects in most other tissues (17). Raloxifene prevents early postmenopausal bone loss in women and reduces the rate of vertebral fractures in women with postmenopausal osteoporosis (18, 19). Less is known about the efficacy of raloxifene in men.
In this study, we evaluated the effects of raloxifene on bone mineral density in men receiving a GnRH agonist for nonmetastatic prostate cancer.
| Subjects and Methods |
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Study participants were recruited at Massachusetts General Hospital (Boston, MA) between February 2000 and February 2002. All subjects were receiving treatment with a GnRH agonist for prostate cancer for 6 months or more at study entry. Subjects had a radionuclide bone scan within 6 months of initiating GnRH agonist treatment or 6 months before study entry. Men with bone metastases or evidence of progressive disease (serum prostate-specific antigen >150% nadir value) were excluded. Men with metabolic bone disease, history of treatment for osteoporosis, history of deep venous thrombosis or pulmonary embolus, serum calcium less than 8.4 or more than 10.6 mg/dl, or serum creatinine concentration more than 2.0 mg/dl (177 µmol/liter) were also excluded.
Study design
After a screening visit, eligible subjects were assigned randomly using computer-generated cards to receive raloxifene (Evista, Eli Lilly and Co., Indianapolis, IN; 60 mg by mouth daily) or no raloxifene for 12 months. Subjects were aware of their treatment assignment. Compliance was assessed with patient diaries. Subjects in both groups continued treatment with a GnRH agonist. All subjects received calcium carbonate (500 mg daily) and a daily multivitamin containing 400 IU vitamin D. There was no required run in period. Study personnel who performed or analyzed the main study outcomes were blinded to the treatment assignments.
After randomization, subjects were evaluated at the Mallinckrodt General Clinical Research Center at Massachusetts General Hospital at baseline, 6, and 12 months. Serum and urine samples were obtained at each visit and stored at 80 C. Bone mineral density and body composition were measured by DXA at baseline, 6, and 12 months. The institutional review board of Dana Farber Partners Cancer Care approved the study. All subjects gave written informed consent.
Study endpoints
The bone mineral density of the posteroanterior lumbar spine and proximal femur was determined by DXA using a Hologic QDR 4500A densitometer (Hologic, Inc., Waltham, MA). Lean and fat mass were also determined by DXA (software version 11.2, Hologic, Inc.).
Serum concentrations of testosterone (Diagnostic Products, Los Angeles, CA), estradiol (Nichols Institute, San Juan Capistrano, CA), 25-hydroxyvitamin D (DiaSorin, Stillwater, MN), PTH (Nichols Institute), and amino-terminal propeptide of type I collagen (DiaSorin) were measured by RIAs or immunoradiometric assays. The lower limits of detection for serum testosterone and estradiol were 6 ng/dl (0.2 nmol/liter) and 3 pg/ml (11 pmol/liter), respectively. Urinary deoxypyridinoline (Metra Biosystems, Mountain View, CA) was measured by enzyme immunoassay. Serum cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and triglyceride concentrations were measured by colorimetric enzymatic assays on an automated clinical chemistry analyzer (Roche Diagnostics/Roche Molecular Biochemicals, Indianapolis, IN).
Statistical analyses
The primary study endpoint was the percent change in the bone mineral density of the posteroanterior lumbar spine from baseline to 12 months. The power calculations for this study assume a 3.0% SD of the change from baseline (2) and dropout rate of 20%. The sample size of 48 subjects (24 subjects/group) provides 80% power to detect a difference of at least 2.8% using a two-sided t test (
= 0.05). Percent changes in bone mineral density, body composition, gonadal steroids, and biochemical markers of bone turnover from baseline to 12 months were compared between groups using t tests (20). All data were included in the efficacy analyses, including data from subjects who discontinued treatment early.
Statistical analyses were performed using SAS version 8.1 (SAS Institute, Inc., Cary, NC). Values are reported as means ± SE unless specified otherwise. All P values are two sided, and values less than 0.05 are considered statistically significant.
| Results |
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Forty-eight eligible subjects were recruited between February 2000 and February 2002. Forty-four subjects completed the baseline evaluation (Fig. 1
). Baseline characteristics of men assigned to raloxifene and men assigned to no raloxifene were similar (Table 1
).
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Gonadal steroids
Mean serum testosterone levels at baseline were in the castrate range in both groups (Table 1
). Changes in serum total testosterone, estradiol, and SHBG levels did not differ significantly between the groups (Fig. 2
).
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The mean (±SE) bone mineral density of the posteroanterior lumbar spine increased by 1.0 ± 0.9% in the men treated with raloxifene and decreased by 1.0 ± 0.6% in the men who did not receive raloxifene (P = 0.07) (Fig. 3A
). The between-group differences in percent change from baseline to 12 months was 2.0% (95% confidence interval, 0.24.0%).
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In men treated with raloxifene, changes in bone mineral density of posteroanterior lumbar spine and total hip did not correlate with either baseline estradiol levels or baseline free estrogen index (data not shown).
Biochemical markers of bone turnover
Serum concentrations of amino-terminal propeptide of type I collagen and urinary excretion of deoxypyridinoline were elevated at baseline (Table 1
). Mean serum concentrations of amino-terminal propeptide of type I collagen decreased by 20.3 ± 9.3% in the men treated with raloxifene and increased by 13.9 ± 11.1% in men who did not receive raloxifene (P = 0.03) (Fig. 4A
). Urinary excretion of deoxypyridinoline decreased by 6.4 ± 7.8% in the men treated with raloxifene and increased by 10.3 ± 5.4% in men who did not receive raloxifene (P = 0.10) (Fig. 4B
). The between-group differences in percent change from baseline to 12 months was 34.2% (95% confidence interval, 4.264.2%) for amino-terminal propeptide of type I collagen and 16.6% (95% confidence interval, 3.737.0%) for urinary excretion of deoxypyridinoline.
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Body composition and serum lipoproteins
Mean changes in body mass index, lean mass, fat mass, and serum lipoproteins did not differ significantly between groups (Table 2
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One man had a pulmonary embolus after 6 months of treatment with raloxifene. Subsequent testing revealed no factors associated with increased thromboembolic risk except for an elevated plasma homocysteine level. There were no other serious treatment-related adverse events.
| Discussion |
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In postmenopausal women, raloxifene decreases markers of both bone formation and bone resorption (18, 21, 22). In our study, raloxifene significantly decreased serum concentration of amino-terminal propeptide of type I collagen, a marker of bone formation. Raloxifene also tended to decrease urinary excretion of deoxypyridinoline, a marker of bone resorption. These preliminary observations suggest that raloxifene increases bone mineral density by similar mechanisms in postmenopausal women and severely hypogonadal men.
Tamoxifen increases bone mineral density in postmenopausal women but decreases bone mineral density in premenopausal women (23, 24). Similarly, the effects of raloxifene on bone mineral density in men may depend on baseline estradiol levels. In our study of severely hypogonadal men (mean serum estradiol, 6 ± 1 pg/ml), raloxifene significantly increased bone mineral density of the hip. In a study of mildly hypogonadal elderly men (mean serum estradiol, 28 ± 2 pg/ml), raloxifene had no significant effect of biochemical markers of bone turnover (25). Changes in bone turnover correlated with baseline estradiol levels, however, suggesting that the efficacy of raloxifene may depend on estradiol levels (25). Baseline estradiol levels did not predict changes in bone mineral density or biochemical markers of bone turnover in our subjects, probably because estradiol levels were uniformly low.
Most other studies of men receiving treatment with a GnRH agonist have evaluated the effects of initial therapy. In contrast, the median duration of prior treatment in our subjects was more than 2 yr. Bone mineral density decreased in our control subjects at similar rate to that reported in men receiving initial GnRH agonist treatment (2). In addition, baseline levels of urinary deoxypyridinoline in our subjects were similar to those reported in men during short-term GnRH agonist treatment (2, 26). These observations suggest that long-term treatment with a GnRH agonist is associated with a persistent high bone turnover state and steady decline in bone mineral density.
In postmenopausal women, raloxifene increases the risk for venous thromboembolic events by approximately 3-fold (19). One subject in our study had a pulmonary embolus. In considering raloxifene for the treatment or prevention of osteoporosis in men with prostate cancer, the potential reduction in fracture risk must be weighed against the increased risk for thromboembolic events.
Bisphosphonates also prevent bone loss in men receiving GnRH agonist therapy for prostate cancer. In two randomized controlled trials, intravenous pamidronate prevented bone loss in men treated with a GnRH agonist (2, 27). In another randomized controlled trial, intravenous zoledronic acid increased bone mineral density in men treated with a GnRH agonist or bilateral orchiectomies (28). Additional studies are needed to compare the efficacy and safety of raloxifene with bisphosphonates in hypogonadal men.
In postmenopausal women, raloxifene significantly decreases serum concentrations of total cholesterol and low-density lipoprotein cholesterol (18). In contrast, raloxifene did not significantly change serum total cholesterol and low-density lipoprotein cholesterol concentrations in our severely hypogonadal male subjects. Raloxifene also had no effect on serum concentrations of total lipid profiles in mildly hypogonadal men (25). Additional studies are needed to determine whether selective estrogen receptor modulators have gender-specific effects on lipoprotein metabolism.
Our study has limitations. Although personnel who performed or analyzed the main outcomes were blinded to treatment assignments to minimize any potential bias, the open-label design may have influenced study outcomes through unintended effects on subject behavior. In addition, the open-label design may have influenced adverse event reporting. The study was designed to compare changes in bone mineral density. Larger studies are required to assess differences in fracture incidence.
In summary, raloxifene significantly increased bone mineral density of the hip and tended to increase bone mineral density of the spine in men receiving a GnRH agonist for prostate cancer. Raloxifene may represent a novel therapy to prevent bone loss in hypogonadal men.
| Acknowledgments |
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| Footnotes |
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Received December 4, 2003.
Accepted May 7, 2004.
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