What the evidence says
Romosozumab decreases vertebral fracture risk in postmenopausal women with osteoporosis. After 12 months, one trial source reports a 73% lower risk of vertebral fracture than the comparator (p < 0.001). Over 3 years, one year of romosozumab followed by two years of denosumab gave a 66% relative risk reduction (incidence 1.0% versus 2.8%; p < 0.001). Romosozumab followed by alendronate gave a 48% lower risk than alendronate alone at 24 months (incidence 6.2% versus 11.9%; p < 0.001). A network meta-analysis puts the odds ratio for bisphosphonates versus romosozumab at 2.06 (95% CI 1.40–3.03), which means higher vertebral fracture risk with bisphosphonates.
The effect at other skeletal sites is smaller or later. At 12 months, romosozumab shows no measured difference in non-vertebral fracture rate. Over 3 years with denosumab follow-up, non-vertebral fracture risk falls by 21% (incidence 3.9% versus 4.9%; p = 0.039). Against alendronate alone, it is 19% lower (incidence 8.7% versus 10.6%; p = 0.04). For hip fracture, romosozumab followed by alendronate gives a 38% lower risk than alendronate alone (incidence 2.0% versus 3.2%; p = 0.02). The network meta-analysis puts the odds ratio for bisphosphonates versus romosozumab at 1.63 (95% CI 1.10–2.42). For romosozumab versus selective oestrogen receptor modulators it is 0.44 (95% CI 0.24–0.81). Clinical fracture risk is 36% lower at 12 months (p = 0.008). Against placebo, the odds ratio for clinical fractures is 0.64 (95% CI 0.47–0.89), equal to 9 fewer clinical fractures per 1000 people. For major osteoporotic fractures it is 0.51 (95% CI 0.33–0.79).
The claims give one mechanism. Romosozumab has a rapid but transient anabolic effect, followed by a sustained antiresorptive phase. The trials that add alendronate or denosumab after romosozumab sit within this sequence, so their results describe the sequence rather than romosozumab alone.
The certainty of these estimates varies. The vertebral estimates against placebo and active comparators come from randomised trials with large effects. The network meta-analysis estimates against selective oestrogen receptor modulators, and for major osteoporotic fractures, rest on few trials and are imprecise. The clinical fracture estimate against placebo rests on only two romosozumab versus placebo trials, with serious risk of bias and imprecision.
Safety data sit alongside the fracture data. One head-to-head randomised trial found a higher incidence of serious cardiovascular events with romosozumab than with alendronate. The claims give no magnitude.
Evidence is thin for fracture outcomes in people with cancer. Preclinical work reports that anti-sclerostin antibody reduces tumor growth in bone and protects bone from cancer-induced destruction in breast cancer. A pilot trial in multiple myeloma has no published results. No human fracture outcome for these groups appears in the claims.
Where the evidence splits
Non-vertebral fracture results differ by timepoint and region. At 12 months there is no measured difference in non-vertebral fracture rate. Over 3 years with denosumab, risk falls by 21%. A post hoc regional analysis found no risk reduction in Latin America and a 42% reduction in the rest of the world (p = 0.012). The claims tie the regional split to background fracture risk. They do not say why the 12-month result is null while the 3-year result is not, and that gap is unexplained by the sources on this page. Differences in follow-up length and added denosumab are design differences, but the sources do not attribute the split to them.
The sources disagree on whether baseline risk changes the size of the effect. One source states that romosozumab's effects are greater the higher the fracture probability at baseline. A meta-regression in another source finds that bone anabolic agents reduced clinical and vertebral fractures irrespective of mean age and baseline risk. The claims give a partial explanation. The meta-regression is observational and vulnerable to aggregation bias and confounding, and the anabolic trials showed a modest spread of baseline risk factors. The first finding comes from a post hoc regional analysis. The claims do not settle which is correct.
Findings
Romosozumab decreases vertebral fracture risk in postmenopausal women with osteoporosis.
confidence — direction: highconfidence — magnitude: highconsensus: settled. Every source points the same way.
- mechanism
- anabolic effect that is rapid but transient, followed by a sustained antiresorptive phase
- effect
- decrease. 73% lower risk at 12 months. After 12 months of romosozumab and then denosumab, the 3-year relative risk reduction is 66% (incidence 1.0% versus 2.8%). Network meta-analysis: bisphosphonates versus romosozumab odds ratio 2.06 (95% CI 1.40–3.03).
- conditions / moderators
- the 3-year figure includes two years of denosumab. The network meta-analysis rates the bisphosphonate comparison moderate certainty, with few direct romosozumab trials and inconsistent vertebral fracture definitions.
Romosozumab followed by alendronate decreases vertebral fracture risk relative to alendronate alone.
confidence — direction: highconfidence — magnitude: highconsensus: settled
- mechanism
- anabolic phase followed by a sustained antiresorptive phase, compared with an antiresorptive alone
- effect
- decrease. 48% lower risk at 24 months (risk ratio 0.52; incidence 6.2% versus 11.9%).
- conditions / moderators
- active-comparator trial in postmenopausal women with osteoporosis. Other moderators not established.
Romosozumab decreases non-vertebral fracture risk over longer follow-up, with no measured effect at 12 months.
confidence — direction: highconfidence — magnitude: mediumconsensus: contested. The 12-month result is null, the longer results are positive, and the regional result differs by region.
- mechanism
- not established for the timing difference
- effect
- no measured effect on non-vertebral fracture rate at 12 months. Over 3 years with denosumab follow-up, relative risk reduction of 21% (incidence 3.9% versus 4.9%). Against alendronate alone, 19% lower risk (incidence 8.7% versus 10.6%).
- conditions / moderators
- a post hoc analysis found no risk reduction in Latin America and a 42% reduction in the rest of the world (p = 0.012). The claims tie this to regional background fracture risk.
Romosozumab decreases hip fracture risk relative to alendronate alone, oral bisphosphonates, and selective oestrogen receptor modulators.
confidence — direction: high for alendronate and oral bisphosphonates; medium for selective oestrogen receptor modulatorsconfidence — magnitude: medium for alendronate and oral bisphosphonates; low for selective oestrogen receptor modulatorsconsensus: settled for direction against alendronate and oral bisphosphonates. Thin against selective oestrogen receptor modulators.
- mechanism
- not established separately for the hip site
- effect
- decrease. After romosozumab then alendronate, 38% lower risk than alendronate alone (incidence 2.0% versus 3.2%). Bisphosphonates versus romosozumab odds ratio 1.63 (95% CI 1.10–2.42). Romosozumab versus selective oestrogen receptor modulators odds ratio 0.44 (95% CI 0.24–0.81).
- conditions / moderators
- hip fracture reporting is inconsistent across trials. The selective oestrogen receptor modulator comparison has very limited direct evidence and imprecise estimates.
Romosozumab decreases clinical and major osteoporotic fracture risk relative to placebo.
confidence — direction: high for clinical fractures; medium for major osteoporotic fracturesconfidence — magnitude: high for the 12-month clinical fracture figure; low for the network meta-analysis estimatesconsensus: settled for direction. Thin on magnitude.
- mechanism
- not established
- effect
- decrease. Clinical fractures: 36% lower risk at 12 months (p = 0.008). Network meta-analysis odds ratio 0.64 (95% CI 0.47–0.89), equal to 9 fewer clinical fractures per 1000 people. Major osteoporotic fractures odds ratio 0.51 (95% CI 0.33–0.79).
- conditions / moderators
- only two romosozumab versus placebo trials. The network meta-analysis reports serious risk of bias and imprecision. Major osteoporotic fractures appear in few trials with varying definitions.
Whether the size of the fracture reduction depends on baseline fracture risk is mixed evidence.
confidence — direction: mediumconfidence — magnitude: lowconsensus: contested
- mechanism
- not established
- effect
- mixed evidence. One source reports greater effects at higher baseline fracture probability. A meta-regression reports reductions in clinical and vertebral fractures irrespective of mean age and baseline risk.
- conditions / moderators
- the meta-regression is observational and vulnerable to aggregation bias and confounding. The anabolic trials had a modest spread of risk factors. The regional post hoc analysis is the other evidence for modification.
Romosozumab increases serious cardiovascular events relative to alendronate.
confidence — direction: highconfidence — magnitude: highconsensus: thin. The claims cite one head-to-head trial.
- mechanism
- not established in the claims
- effect
- increase in incidence of serious cardiovascular events in one head-to-head randomised trial. No magnitude in the claims.
- conditions / moderators
- the source advises avoiding romosozumab in patients at high risk of myocardial infarction or stroke.
Romosozumab's effect on fracture in people with cancer is unmeasured in humans.
confidence — direction: high for the preclinical finding; medium for the absence of human resultsconfidence — magnitude: medium for the preclinical finding; low for human resultsconsensus: thin
- mechanism
- preclinical studies show anti-sclerostin antibody reduces tumor growth in bone and protects bone from cancer-induced destruction in breast cancer
- effect
- no measured effect reported in humans. A pilot trial in multiple myeloma has unpublished results.
- conditions / moderators
- the preclinical findings are limited to animal models.