Amgen's (AMGN) - Get Report effort to improve disappointing sales of its multiple myeloma drug Kyprolis took a hit Tuesday with the failure of a phase III clinical trial involving newly diagnosed patients.

The addition of Kyprolis to a chemotherapy backbone did not slow the regrowth of tumors any better than Velcade plus the same chemotherapy in patients with newly diagnosed multiple myeloma, Amgen said Tuesday.

The phase III "Clarion" study was designed to demonstrate the superiority of Kyprolis over Velcade, sold by the Japanese pharma giant Takeda. Instead, progression-free survival for Kyprolis patients was 22.3 months compared to 22.1 months for the Velcade arm.

An analysis of overall survival from the study is not yet mature but at an interim look, Velcade patients were living longer than Kyprolis patients, Amgen said.

Amgen acquired Kyprolis when it bought Onyx Pharmaceuticals for $10 billion in 2013. The drug is approved for the treatment of multiple myeloma in patients who no longer respond to initial therapy. Kyprolis sales of $326 million in the first half of 2016 and $512 million in 2015 have been a disappointment, particularly compared against the large price tag paid for Onyx.

Finding a place for Kyprolis in the treatment of newly diagnosed multiple myeloma patients was supposed to help accelerate sales and justify the Onyx acquisition. The failure of the Clarion study sets Amgen back, although additional front-line studies are still underway.

Multiple myeloma has become a very competitive treatment market in recent years. Celgene (CELG) - Get Report dominates with two drugs, Revlimid and Pomalyst and Takeda's Velcade holds its own. Most recently, two new drugs, Darzalex from Johnson & Johnson (JNJ) - Get Report and Empliciti from Action Alerts PLUS holding Bristol-Myers Squibb (BMY) - Get Report have entered the fray. Doctors use combinations of drugs to treat multiple myeloma patients, so Amgen can ill afford to lose ground to its competitors.

Amgen closed Monday at $173.53, ahead of Tuesday's Kyprolis setback.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.