Amgen's (NASDAQ:AMGN) high-profile acquisition of Onyx Pharmaceuticals this summer put it knee-deep in the hunt for next-generation therapies for multiple myeloma. That's great news for patients given recent results from mid-stage trials combining Amgen's newly acquired Kyprolis with Celgene's (NASDAQ:CELG) Revlimid.

Kyprolis is growing and may grow more
Kyprolis is a high-profile multiple myeloma drug approved by the Food and Drug Administration in July 2012. Analysts believe Kyprolis may eventually generate up to $3 billion in annual sales as its label expands to include new indications.

So far, Kyprolis is generating respectable sales growth. During the third quarter, it generated $65 million in sales, up 6% from the second quarter. Currently, Amgen is studying the drug as both a first and second line treatment for multiple myeloma. If successful, Kyprolis patient pool would stand to climb markedly.

In phase 2 trials, combining Kyprolis with Celgene's multiple myeloma blockbuster Revlimid and corticosteroid Dexamethasone, or Dexa, produced strong results in relapsed multiple myeloma patients. 77% of patients responded to the combination therapy, with patients seeing benefits as soon as one month. Importantly, the positive response to the drug showed persistence, with median duration reaching 22 months.

What makes this combination attractive is the efficacy in hard-to-treat relapsed patients. As was pointed out by the Myeloma Beacon, one-quarter of patients were resistant to Takeda's Velcade and almost half hadn't succeeded when previously treated with Celgene's Revlimid. Currently, Kyprolis is only approved as a treatment of multiple myeloma patients who had failed on two or more other drugs and relapsed within 60 days.

As a result of the positive phase 2 data, Amgen is moving the drug cocktail into phase 3, comparing it head to head with a combination of Revlimid and Dexa.

Is that bad news for Celgene?
Advancing Kyprolis head-to-head against a Revlimid cocktail may imply that Revlimid could be at risk. But, given that Kyprolis' combination therapy includes Revlimid, it's more likely it simply encourages oncologists to use the drug. That could mean Revlimid actually gains sales against Velcade because 27% of the patients in the phase 2 study hadn't been previously treated with Revlimid. 86% of those previously untreated Revlimid patients had a positive response in the trial, and the median duration of response hadn't been reached when study data was released.

Comparing the study to other three drug studies -- including a Revlimid, Velcade, and Dexa phase 2 trial -- suggests that the Kyprolis, Revlimid and Dexa therapy is superior, according to the Myeloma Beacon. They drew their conclusion by comparing both response rates and levels of peripheral neuropathy, or nerve pain.

Celgene, not Amgen, may also benefit from another promising candidate, AbbVie (NYSE:ABBV) and Bristol-Myers Squibb's (NYSE:BMY) elotuzamab. AbbVie and Bristol are co-developing the mutliple myeloma drug and a phase 2 study of it, combined with Revlimid and dexa was promising. In that trial, 90% of patients receiving the AbbVie and Bristol combination responded and median duration for progression free survival hadn't been reached when the data had originally been reported. Bristol is also advancing early stage studies for elotuzamab with PDL Biopharma.

The opportunity to advance new therapies is significant
Multiple myeloma is the second most common blood cancer in the United States, and sadly most of those treated with existing therapy relapse and require additional treatment.

Approximately 20,000 people are diagnosed with the disease in the United States annually and some 750,000 people are diagnosed globally. Unfortunately, the incidence rate has climbed over the past twenty years to 6.36 cases per 100,000 in 2010 versus 5.6 cases per 100,000 in 1993. Thankfully, new treatments are reducing patient mortality and additional advances, such as these, may further improve survival.

Foolish final thoughts
Kyprolis isn't a cheap drug. When it was launched in 2012, its $10,000 price tag for a 28-day cycle made it the most expense of the multiple myeloma treatments, eclipsing the $4,000 to $8,000 price for Velcade, and $8,000 price for a 21-out-of-28-day dosing of Revlimid. As a result, Amgen's opportunity to grow sales by expanding its label to include more patients could be significant.  So investors should keep a close eye on Kyprolis' trial data because it could materially boost or limit Amgen's growth.