The Oncologist, Vol. 13, No. 2, 187-195, February 2008; doi:10.1634/theoncologist.2007-0152 © 2008 AlphaMed Press
Cancer Treatment-Induced Bone Loss: Pathophysiology and Clinical PerspectivesUniversity of Pittsburgh School of Medicine, Magee-Women's Hospital, Pittsburgh, Pennsylvania, USA Key Words. Androgen deprivation therapy • Aromatase inhibitor • Bisphosphonate • Bone loss • Osteoporosis Zoledronic acid Correspondence: Adam M. Brufsky, M.D., Ph.D., University of Pittsburgh School of Medicine, Magee-Women's Hospital, Suite 4628, Pittsburgh, Pennsylvania 15213, USA. Telephone: 412-641-6500; Fax: 412-641-2296; e-mail: brufskyam{at}upmc.edu Received August 21, 2007; accepted for publication November 10, 2007. Disclosure: A.M.B. has participated in the speakers bureau for Novartis Pharmaceuticals. Funding for medical editorial assistance was provided by Novartis Pharmaceuticals Corporation. No other potential conflicts of interest were reported by the author, planners, reviewers, or staff managers of this article.
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Hormone-ablative therapies for breast or prostate cancer can cause marked and rapid reductions in circulating estrogen or testosterone levels, resulting in significant effects on bone metabolism and cancer treatment–induced bone loss (CTIBL). Most patients with cancer are over the age of 65 and are already at risk for osteoporosis. Thus, accelerated bone loss from CTIBL is especially concerning in this population. Although there are currently no approved therapies for the treatment or prevention of CTIBL, oral bisphosphonates have been used in settings other than oncology to treat bone loss. New-generation i.v. bisphosphonates have demonstrated promising activity in preventing CTIBL in patients receiving hormonal therapy for breast or prostate cancer. In particular, zoledronic acid not only prevents CTIBL in both breast and prostate cancer patients but also increases bone mineral density above baseline. Such agents have the potential to delay or prevent CTIBL in patients receiving hormonal therapies.
Patients with early-stage breast cancer or high-risk prostate cancer are often treated with antihormonal therapy to inhibit disease progression or prevent disease recurrence. Such therapies include gonadotropin-releasing hormone (GnRH), luteinizing hormone-releasing hormone (LHRH) agonists, antiandrogens (e.g., bicalutamide, flutamide), and aromatase inhibitors (AIs) [1, 2]. These therapies can lead to bone metabolism changes, resulting in loss of bone mass [3]. AIs and androgen deprivation therapy (ADT) deplete the circulating levels of estrogen and testosterone that maintain bone mass through suppression of bone resorption and promotion of bone formation [3, 4]. Early treatment with bisphosphonates may preserve skeletal integrity throughout disease progression by preventing bone loss and decreasing fracture risk [1, 5, 6]. Cancer treatment-induced bone loss (CTIBL) increases the risk for skeletal morbidity [7]. An understanding of CTIBL is critical for determining how to assess the risk and identifying which patients may benefit from preventive therapy. This information can guide screening and early intervention with therapies such as bisphosphonates, which have become the standard of care for reducing the risk for skeletal complications in patients with metastatic bone disease. Current American Society of Clinical Oncology (ASCO) guidelines and expert panels suggest that patients with bone metastases from breast or prostate cancer should receive bisphosphonates from the time of diagnosis [5, 6]. Preclinical and clinical data show that bisphosphonates can also prevent and treat CTIBL in patients with breast and prostate cancer, and bisphosphonates may inhibit malignant bone disease development in patients with early-stage cancer. Consistent with these findings, bisphosphonates are recommended for bone loss prevention in patients with prostate cancer receiving ADT [1]. Guidelines for the prevention of CTIBL in patients with breast cancer have not yet been established. This review focuses on CTIBL in patients with breast and prostate cancer and data from clinical trials that evaluate the effectiveness and safety of bisphosphonates for the prevention and treatment of CTIBL.
Women with breast cancer have an increased risk for osteoporosis because of treatment-induced premature ovarian failure and the direct effects of cytotoxic chemotherapy [8]. Estrogens limit bone resorption, and decreases in available estradiol levels can accelerate bone resorption, resulting in overall bone loss [3]. Greater than 60% of women with breast cancer experience ovarian failure within 1 year of beginning postoperative adjuvant chemotherapy regimens [3]. Studies have shown that chemotherapy-induced menopause, either temporary or permanent, is associated with significant bone loss. Reductions in bone mineral density (BMD) of the spine (6%–7.5%) and femoral neck (2%–4.5%) have been reported within 1 year of initiation of adjuvant chemotherapy for breast cancer [9, 10]. In women treated with cyclophosphamide, methotrexate, and 5-fluorouracil chemotherapy who experienced permanent ovarian failure, clinically significant bone loss continued during the 2–5 years following chemotherapy [11].
Ovarian suppression in premenopausal women receiving AIs is a major concern because of the near complete elimination of circulating estradiol levels. Long-term use of AIs (e.g., letrozole, anastrozole) is increasing because of their superior efficacy and safety profiles compared with those of tamoxifen [12, 13]. Another important clinical concern in patients with breast cancer is AI-associated bone loss (AIBL), because it is more rapid than bone loss associated with menopause (1.7% and 2.6% loss of total hip and lumbar spine BMD, respectively, during the first year) [14] and the severity increases with treatment duration. The Anastrozole, Tamoxifen, Alone or in Combination (ATAC) trial in postmenopausal women with early-stage breast cancer demonstrated the superiority of AIs over tamoxifen for disease-free survival (hazard ratio [HR], 0.86; p = .03) and time to disease recurrence (HR, 0.83; p = .015) [12]. Although the anastrozole safety profile was better than that of tamoxifen overall, anastrozole was associated with a greater fracture incidence (11% versus 7.7%, respectively) [12]. Assuming a baseline annual fracture rate of 17 fractures per 1,000 healthy postmenopausal women, survivors of breast cancer not treated with adjuvant hormonal therapy have a relative fracture risk of 1.15 (20 fractures per 1,000 women) [15]. Based on the ATAC trial, patients with breast cancer treated with anastrozole have a relative fracture risk of 1.36 (23 fractures per 1,000 women). This translates into two additional fractures per year in 300 postmenopausal women with early breast cancer. In contrast, patients treated with tamoxifen have a relative fracture risk of only 0.91, suggesting that tamoxifen may have bone-protective effects. Bone loss and fracture risk were also analyzed retrospectively in a patient-claims database of women with early-stage breast cancer and no osteoporosis who received an AI (n = 1,354) or did not (n = 11,014) [16]. The prevalence of osteoporosis was 8.7% in the AI group versus 7.1% in the control group (p = .01), and the risks for both bone loss and fracture were significantly higher in the AI group than in the control group (27% and 21%, respectively; p = .02) (Fig. 1) [16].
A recent study of anastrozole versus tamoxifen as adjuvant therapy in patients with breast cancer receiving goserelin (n = 197) demonstrated that overall bone loss was significantly greater after 3 years of anastrozole treatment compared with tamoxifen (–14.4% and –11.6%, respectively; p < .001) [17]. Letrozole has also recently been shown to result in significantly greater loss of BMD in the total hip (–3.6%, versus –0.71% for placebo; p = .044) and lumbar spine (–5.3% versus –0.70% for placebo; p = .008) after 2 years of treatment in patients with breast cancer who had previously received 5 years of adjuvant tamoxifen therapy (n = 226) [18]. The nonsteroidal AI exemestane has also been shown to decrease BMD and increase the incidence of fractures. The Intergroup Exemestane Study assessed bone loss and fracture risk among patients with breast cancer who were randomized to tamoxifen or exemestane after 2–3 years of tamoxifen therapy (n = 4,274) [19]. In a subset of patients in whom BMD was assessed (n = 206), BMD significantly decreased from baseline by 2.7% (lumbar spine) and 1.4% (hip) (p < .0001 for both) within 6 months of exemestane treatment. A similar study by Gonnelli et al. [20] showed that patients receiving exemestane for 2 years had significant reductions in lumbar spine (–2.99; p < .01), femoral neck (–1.92; p < .01), and total hip (–2.01; p < .05) BMD. Finally, in a 2-year study in lower-risk women with early breast cancer (n = 147) who received either exemestane or placebo, the exemestane group had a significantly higher mean annual loss of femoral neck BMD than the placebo group (2.72% versus 1.48%, respectively; p = .024) [21]. However, the mean annual loss in lumber spine BMD did not reach significance (exemestane, 2.17%; placebo, 1.84%; p = .568). Earlier studies have been reviewed previously [22], and their results provide ample evidence that AI treatment in women with breast cancer may lead to deleterious effects on bone health.
Androgen deprivation–induced bone loss is a significant clinical concern in patients with hormone-sensitive prostate cancer receiving long-term ADT. ADT decreases circulating levels of estrogen and testosterone, both of which maintain bone mass through suppression of bone resorption and promotion of bone formation [3, 23]. Thus, similar to AIs in breast cancer, ADT ultimately accelerates bone loss beyond the levels seen with aging (1%–2% per year) [2, 4]. This is especially concerning because patients with prostate cancer typically have low BMD even before receiving ADT either because of age, underlying disease, or other comorbidities [1]. In a study of men with advanced prostate cancer for >2 years before initiation of ADT (n = 174), 42% were osteoporotic compared with 27% of age-matched controls (n = 106; p = .022) [24].
Long-term ADT is associated with significant and progressive decreases in BMD that correlate with duration of therapy [25, 26], and the risk for fragility fractures increases as BMD decreases [27]. In a retrospective analysis of patient-claims data (Medicare) from 1992–2001 (n = 4,494), ADT increased the risk for osteopenia/osteoporosis (30%) and pathologic and nonpathologic fractures (16% and 42%, respectively) [28]. In another retrospective analysis of patient databases (Surveillance, Epidemiology, and End Results program and Medicare) from 1992–1997 (n = 50,613), 19.4% of patients with prostate cancer receiving ADT for Reducing bone loss is critical because fractures significantly correlate with shorter survival in men with prostate cancer [33]. When fracture history was evaluated in men with prostate cancer undergoing ADT (n = 195), the median overall survival time was 39 months longer in men without a history of skeletal fracture than in men with no prior fracture (p = .004) [33].
Breast Cancer The ASCO guidelines recommend strategies for the management of bone health in patients with breast cancer [5]. Osteoporosis screening should begin at age 65 or at age 60 for women with an increased osteoporosis risk [5]. Supplementation with calcium (1,200 mg/day) and vitamin D (800 IU) is also recommended for patients at risk for osteoporosis because these levels prevent decreases in femoral neck BMD and reduce the risk for hip fractures in elderly women [34–36]. Bisphosphonates (alendronate or risedronate) are also recommended for high-risk patients with breast cancer and T-scores of –2.5 or less [5]. A T-score represents the difference between a patient's BMD measurement and the mean BMD of young healthy adults and is expressed as a multiple of the standard deviation (SD) from the mean [3]. This classifies patients as normal (greater than –1 SD), osteopenic (–1 to –2.5 SD), or osteoporotic (less than –2.5 SD) and can provide an estimate of fracture risk [3, 37]. There are currently no approved treatment or prevention therapies for CTIBL or AIBL in patients with breast cancer [38]. However, both clodronate and risedronate have been shown to decrease the bone loss associated with chemotherapy-induced ovarian failure [9, 39]. In separate randomized, placebo-controlled trials, 2 years of oral clodronate (1,600 mg/day) or oral risedronate (30 mg/day during the first 2 weeks of a 12-week cycle) treatment resulted in less lumbar spine and femoral neck bone loss than in controls [9, 39]. At 2 years, in patients who experienced ovarian failure, oral clodronate resulted in a 38% lower mean lumbar spine bone loss and a 91% lower mean femoral neck bone loss than in the control group [9]. No specific adverse events (AEs) were listed, and no significant differences in AEs between treatment groups were reported. No renal impairment was observed during the study. However, one patient interrupted clodronate treatment because of diarrhea. In a similar study with oral risedronate, the mean lumber spine and femoral neck bone loss was significantly lower, by 2.5% (p = .041) and 2.6% (p = .029), respectively, than with placebo [39]. Risedronate also produced a significantly lower trochanter bone loss, by 3.1%, compared with placebo (p = .002). At 3 years (1 year after treatment ended), differences in BMD remained significant at the lumbar spine (p = .024), femoral neck (p = .011), and trochanter (p = .008). The majority of AEs were reported to be mild and similar between the treatment groups. The most common AEs were flu-like symptoms, which occurred predominantly during the first cycle of therapy. No severe upper gastrointestinal AEs were observed. These studies demonstrate that oral bisphosphonates may reduce the bone loss resulting from cancer therapies, but bone integrity was not fully protected. The i.v. bisphosphonate zoledronic acid (Zometa®; Novartis Pharmaceuticals Corporation, East Hanover, NJ), has shown clinical benefits in the treatment of bone metastases among patients with solid tumors. Phase III studies demonstrated that zoledronic acid (4 mg) resulted in a significantly lower risk for developing skeletal-related events (SREs) such as pathologic fractures, by 31%–41% compared with placebo (p < .02 for all studies) [40–42]. Zoledronic acid has also been directly compared with pamidronate in patients with breast cancer, wherein zoledronic acid reduced the risk for an SRE by an additional 16% compared with pamidronate (p = .03) [43]. In a Cochrane review that assessed all approved oral and i.v. bisphosphonates for breast cancer treatment, zoledronic acid produced the largest reduction in the risk for SREs versus placebo (41% versus 14%–23% for ibandronate, clodronate, and pamidronate) [44]. Three clinical trials demonstrated that zoledronic acid may be effective in counteracting AIBL in premenopausal women receiving adjuvant endocrine therapy for hormone-responsive breast cancer. A randomized, open-label, phase III, four-arm trial (the Austrian Breast and Colorectal Cancer Study Group [ABCSG] trial ABCSG 12) in premenopausal women receiving goserelin (3.6 mg/month) compared tamoxifen (20 mg/day) with anastrozole (1 mg/day) with or without zoledronic acid (4 mg i.v. every 6 months) for 3 years after primary surgery for stage I or II estrogen- and/or progesterone-receptor–positive breast cancer [17]. In a subprotocol (n = 401), serial BMD measurements were taken at 0, 6, 12, 24, and 36 months. Women receiving anastrozole for 3 years had greater bone loss than patients receiving tamoxifen (17.3% versus 11.6% decrease in BMD, respectively) [17]. In contrast, the addition of zoledronic acid (4 mg i.v. every 6 months over 3 years) to either treatment regimen effectively inhibited bone loss in the lumbar spine and trochanter. Zoledronic acid also led to significantly better lumbar spine T-scores versus those of patients treated with goserelin plus anastrozole alone (p < .0001) (Fig. 2) [17]. Zoledronic acid combined with endocrine therapy was well tolerated, and there was no observed additive toxicity between zoledronic acid and either goserelin plus anastrozole or goserelin plus tamoxifen. The majority of AEs associated with zoledronic acid were mild to moderate flu-like symptoms (nausea, vomiting, fever, and myalgia), primarily limited to the first dose. There were no clinically relevant changes in serum creatinine, including no increases 1.5x the upper limit of normal, and no reported cases of osteonecrosis of the jaw (ONJ).
In the Zometa®/Femara® Adjuvant Synergy Trial (Z-FAST), zoledronic acid also appeared to prevent AIBL in postmenopausal women with stage I–IIIa estrogen- and/or progesterone-receptor–positive breast cancer receiving adjuvant letrozole (n = 602) [45]. Three hundred one patients received upfront zoledronic acid (4 mg i.v. every 6 months). The other 301 women in the delayed arm of the trial received zoledronic acid only if their T-score at the lumbar spine or total hip decreased below –2.0 SD or if they had a clinical fracture. The primary endpoint was percent change in lumbar spine BMD at 1 year; secondary endpoints were percent change in lumbar spine and total hip BMD at 5 years, change in biochemical markers of bone metabolism, incidence of fractures at 3 years, and time to disease recurrence/relapse. After 1 year of zoledronic acid treatment (4 mg i.v. every 6 months), the lumbar spine and total hip BMD increased by 2.0% and 1.4%, respectively (Fig. 3) [45]. In contrast, among women in the delayed arm of the trial, BMD decreased substantially by 2.6% and 2.1% in the lumbar spine and total hip, respectively. At 1 year, there was also a significant difference in biochemical markers of bone metabolism. In the upfront group at 1 year, levels of the osteolysis and osteogenesis markers N-telopeptide of type I collagen (NTX) and bone-specific alkaline phosphatase (BALP) were significantly reduced by 15% (p < .0001) and 9% (p = .0006), respectively. In contrast, both NTX and BALP had significantly increased by 20% (p = .013) and 24% (p < .0001), respectively, in the delayed group. Adverse events were similar between treatment groups, although bone pain was more common with upfront (11.3%) than with delayed (4%) zoledronic acid. There were no grade 3 or 4 serum creatinine increases (>3.0x the upper limit of normal), and one grade 1 serum creatinine increase in the upfront group (<1.5x the upper limit of normal). There were no reported ONJ cases during the study. A similar, larger trial in Europe (ZO-FAST) (n = 1,066) can significantly detect a 3% BMD change [46]. Results are anticipated this year and may support a strategy of proactive prevention of bone loss (i.e., upfront treatment with zoledronic acid).
Prostate Cancer The National Comprehensive Cancer Network guidelines for prostate cancer recommend considering bisphosphonate therapy in men receiving ADT who are osteopenic or osteoporotic [47]. Supplementation with calcium (500 mg/day) and vitamin D (400 IU) is also recommended for all men undergoing ADT, regardless of BMD.
Oral alendronate and risedronate are used to prevent or treat bone loss in men with osteoporosis [2]. However, recent trials of oral bisphosphonates for the prevention of CTIBL have yielded mixed results. In a retrospective review of men receiving oral alendronate or risedronate, the majority of patients had a decrease in BMD [48]. In contrast, in a study in men with nonmetastatic prostate cancer receiving ADT (n = 112), once-weekly alendronate significantly increased BMD in the spine and femoral neck (3.7% and 1.6% versus baseline, respectively; p
Because bone loss during ADT is more severe than that associated with aging, more frequent administration of an i.v. bisphosphonate may provide greater benefit. Both zoledronic acid and pamidronate (i.v. once every 3 months) prevented androgen deprivation–induced bone loss in the hip and lumbar spine in men with nonmetastatic prostate cancer receiving a GnRH agonist [52, 53]. In contrast with pamidronate, zoledronic acid increased BMD. Versus baseline, the mean BMD in the lumbar spine increased by 5.6% in men receiving zoledronic acid and decreased by 2.2% in placebo-treated men (p < .001 versus placebo) (Fig. 4) [52]. Results were similar in the trochanter and total hip (p < .001 versus placebo). The majority of AEs were similar between the treatment and placebo groups. The most frequently reported AEs were hot flushes, fatigue, and arthralgia. Even a single dose of zoledronic acid has been shown to significantly increase BMD of the total hip and spine at 1 year (p < .001 for both) [54]. In a placebo-controlled trial in men with nonmetastatic prostate cancer treated with a GnRH, one infusion of zoledronic acid (4 mg i.v.) increased the mean BMD of the lumbar spine by 4.0% compared with a decrease of 3.1% in men receiving placebo (p < .001) [55]. Zoledronic acid also prevented bone loss in hormone-naive patients with nonmetastatic prostate cancer treated with goserelin acetate, a synthetic LHRH analogue (n = 200) [56]. At 1 year (n = 140), the mean BMD in the lumbar spine, femoral neck, and hip decreased from baseline (up to 2%) in patients treated with goserelin alone, whereas BMD significantly increased (up to 3.3%) in patients treated with zoledronic acid (4 mg i.v.) every 3 months (p
Safety considerations for oral bisphosphonates include gastrointestinal AEs such as esophagitis and dysphagia [58, 59]. Intravenous bisphosphonates have dose- and infusion rate–dependent effects on renal function and acute-phase (flu-like) reactions associated with the first infusion [58]. Recently, ONJ, characterized by the presence of exposed bone in the oral cavity, has been reported as an uncommon event in patients with cancer who are receiving treatment regimens that include i.v. bisphosphonates and in a very small number of patients receiving oral bisphosphonates for indications other than cancer [60]. However, there is limited prospective data on ONJ in the oncology setting, and only a few retrospective analyses of ONJ in the osteoporosis setting. For example, a retrospective analysis in Australia (2004–2005) reported a 0.88%–1.15% frequency of ONJ among patients with malignant bone disease from cancer and a frequency of only 0.01%–0.04% among patients with osteoporosis receiving a bisphosphonate [61]. Therefore, the frequency of ONJ appears to be lower among patients without malignant bone disease compared with patients who have advanced cancer. Patients with advanced cancer typically have more frequent bisphosphonate dosing and multiple factors that have been associated with a higher risk for ONJ, including the effects of cancer itself, systemic chemotherapeutic regimens, and glucocorticoid treatment [59, 62].
CTIBL is prevalent in patients with breast cancer receiving combination endocrine treatment and in patients with prostate cancer receiving ADT and is typically more severe than bone loss associated with the aging process or menopause [2, 4, 14]. This decrease in BMD increases the risk for fractures, which are associated with chronic pain, loss of mobility, and shorter survival [3, 33]. Bisphosphonates have been demonstrated to be promising in preventing CTIBL in patients with breast or prostate cancer [63, 64]. Early intervention with zoledronic acid prevents bone loss in patients with breast and prostate cancer [17, 45, 52]. Serum creatinine increases and uncommon events such as ONJ have been reported in patients with advanced cancer metastatic to bone; these patients have a greater number of potential risk factors for such AEs than patients in the AIBL setting. The studies presented here have shown that renal AEs are rare, and there have been no cases of ONJ reported to date during zoledronic acid treatment for AIBL. This improved safety profile is likely related to the relatively infrequent administration of zoledronic acid (every 3–6 months versus every 3–4 weeks) and the earlier stage of the cancers in these settings. Ongoing trials are investigating the optimum zoledronic acid regimen in this setting. Current guidelines recommend that patients with bone metastases from breast or prostate cancer receive bisphosphonates from the time of diagnosis. Although proactive use of bisphosphonates in the AIBL and CTIBL settings in breast cancer is not currently included in society guidelines, regulatory approval of zoledronic acid in the AIBL setting is under consideration in both the U.S. and Europe. Furthermore, bisphosphonates are recommended for the prevention of bone loss in patients with prostate cancer receiving ADT [47].
We thank Tamalette Loh, Ph.D., ProEd Communications, Inc.®, for her medical editorial assistance with this manuscript.
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