Analysts may have to wait for detailed data to be presented at an upcoming medical meeting to tease out the market potential for Radius Health Inc.'s subcutaneous abaloparatide in postmenopausal osteoporosis, but the good news is that the Waltham, Mass.-based company's synthetic peptide analogue of human parathyroid hormone-related protein solidly hit its primary endpoint in a phase III trial.

The news sent shares of Radius (NASDAQ:RDUS) up $5.42, or 17 percent, to close Monday at $37.45. The stock has gained nearly 350 percent since its June debut. (See BioWorld Today, June 9, 2014.)

Abaloparatide-SC showed a statistically significant 83 percent reduction in the incident of vertebral fractures vs. the placebo group (p <0.0001) in the phase III trial dubbed ACTIVE. It also appeared to show a numerically greater reduction in fracture rate compared to the open-label comparator arm testing Forteo (teriparatide [rDNA origin]), which demonstrated a 78 percent reduction of incident vertebral fractures vs. placebo (p < 0.0001).

Superiority compared to Forteo – currently the only anabolic osteoporosis treatment on the market, with 2013 sales of more than $1.2 billion – isn't a requirement for abaloparatide-SC's approval. But a lower fracture rate, plus better results in bone mineral density (BMD) measures and fewer side effects will be key points for differentiating abaloparatide-SC in the marketplace.

Comparative analyses of BMD secondary endpoints showed a percent change in BMD from baseline in lumbar spine at 18 months for abaloparatide-SC, Forteo and placebo of 11.20, 10.49 and 0.63, respectively. Total hip percent change in BMD from baseline at 18 months was 4.18, 3.26 and -0.10, respectively, while femoral neck percent change in BMD at 18 months was 3.60, 2.66 and -0.43, respectively.

Adverse events for abaloparatide-SC were consistent with previous studies and were fairly comparable with Forteo, though Radius' drug had slightly lower rates of hypercalciuria (10.9 percent vs. 12.5 percent) and slightly higher rates for dizziness (10 percent vs. 7.3 percent)

On the secondary endpoints as compared to placebo, abaloparatide-SC achieved a statistically significant fracture-rate reduction of 43 percent in the adjudicated nonvertebral fracture subset of patients; a statistically significant reduction of 41 percent in the adjudicated clinical fracture group, which includes both vertebral and nonvertebral fractures; and a statistically significant difference in the time to first incident nonvertebral fracture in both the adjudicated nonvertebral fracture and the clinical fracture subset of patients.

Only secondary endpoints showing statistical significance have been disclosed at this time, said Robert E. Ward, Radius' president and CEO. More data will be forthcoming later.

"The powering was really focused on the primary endpoint," Ward told investors and analysts on an early Monday conference call. "We believe [the clinical and safety data] will reinforce the emerging profile of abaloparatide and eagerly await the first six months data from the ongoing ACTIVExtend trial, which we expect in the second quarter of 2015," he added.

About 91 percent of eligible patients from the ACTIVE study enrolled in the extension study, which will evaluate the reduction in incident vertebral and nonvertebral fractures at up to 24 months as the key endpoints.

Ward said it's too early at this time to gauge market potential of abaloparatide-SC. "Our next step will be to complete ACTIVEextend," he said. With the totality of 24-month data in hand, the firm will be ready to submit marketing applications in both the U.S. and Europe in the second half of next year.

After that, Radius' next step will be to negotiate with regulators on the drug's label. "At that time, we'll be in a better position to assess market penetration," he said.

In the meantime, the company is advancing its transdermal (TD) version of abaloparatide, having recently evaluated a number of patch configurations with 3M Drug Delivery Systems sMTS platform, aiming for a comparable profile to the SC formulation. Ward said Radius sees abaloparatide-TD as a potential post-approval line extension for the franchise.

Elsewhere in its pipeline, Radius has RAD1901, a tissue-selective estrogen receptor degrader being developed for potential use in metastatic breast cancer. The FDA recently accepted the firm's investigational new drug application for a phase I study testing the drug in postmenopausal women with advanced estrogen receptor-positive and HER2-negative breast cancer. That study is aimed at determining the recommended phase II dose and will include a preliminary evaluation of potential antitumor effect.