Shares of Radius Health (RDUS - Get Report) rose on Tuesday, its fourth gain in the last six trading sessions, amid speculation the drug developer is once again a takeover target in the active biotechnology sector.

The stock gained 1.17, or about 2.2%, to $53.54 in over-the-counter trading yesterday. The stock has gained $6.53 since Aug. 1, up about 14%, and up about 38% since mid-July. The stock moves have been fueled more by prospects of the company getting bought than by its actual finances: the company hasn't posted any positive net income since at least 2010.

Still, in the biotechnology universe, a drug maker's product portfolio is often regarded as more important than the fundamentals, and companies with what could be market-leading solutions are prized.

Last October, British newspapers including the Financial Times suggested that Shire (SHPG) could be interested in making a bid for Radius. The Cambridge, Massachusetts-based company's leading product, abaloparatide, is a once-daily injectable therapy designed to treat osteoporosis, a market that Shire once competed in and may be interested in reentering.

Abaloparatide has fared well in clinical trials, and looks to be the superior product in the treatment of osteoporosis, a market that several other drug makers have pursued but with mixed success. The prospect that Radius could bring abaloparatide to the market before the end of the year could improve its prospects as a takeover target.

In addition, Radius may be seeking a partner in Europe to help with the marketing of abaloparatide, president and CEO Robert Ward said this month. Ireland-based Shire, which is reportedly looking for ways to expand beyond its primary product, a treatment for ADHD, might fit that profile. Last year the Irish drug maker made overtures to Baxalta, a company spun off by Baxter (BAX - Get Report) , but the bid was rejected.

Last fall traders speculated that Shire might have been readying a $90 a share bid for Radius, a huge premium for a stock that was, at the time, trading at about $56 a share.

Radius, with a portfolio of development stage products, has no revenues. It has been boosting spending as it prepares for the marketing initiative for abaloparatide. When the company reported results earlier this month, it posted a slightly wider loss than analysts had been projecting, the fifth consecutive quarter in which losses came in ahead of forecasts.

The company's R&D spending also swelled, up 650% year over year, while administration expenses also grew.