What happened

After Amgen (NASDAQ:AMGN) reported impressive data for its AMG 420 in multiple myeloma at the American Society of Hematology Conference (ASH), shares in bluebird bio (NASDAQ:BLUE) were knocked down 19.3% in December, according to S&P Global Market Intelligence.

So what

Multiple myeloma is a hematological cancer with a five-year survival rate of only about 50%, so new treatment options are necessary. One of the most promising next-generation approaches to treating multiple myeloma is chimeric antigen receptor T-cell therapy (CAR-T), which involves engineering T-cells so that they can spot B-cell maturation antigen (BCMA), a protein expressed by multiple myeloma cells.

A man raises his hands in despair as he looks at the monitor on a laptop.

IMAGE SOURCE: GETTY IMAGES.

The CAR-T that's furthest along in clinical trials for multiple myeloma is bluebird bio's bb2121, which is licensed to Celgene (NASDAQ:CELG). The two companies are also studying a second-generation CAR-T, bb21217, and at ASH, investors were given their first look at bb21217's efficacy. In a phase 1 study, the objective response rate in heavily pretreated multiple myeloma patients was 83%.

Although the response rate is impressive for this patient population, bb21217's efficacy failed to significantly improve upon response rates witnessed for bb2121, calling into question just how much better it may prove to be. Adding to the uncertainty was data presented at the conference by Amgen for AMG 420.

AMG 420 is designed to attach together CD3, a protein on the surface of T-cells, and BCMA, allowing the immune system to destroy multiple myeloma cells. At ASH, Amgen reported that, at a dose of 400 micrograms, five of six patients had an objective response. The data suggest that AMG 420 could prove to be a future competitive threat to bb2121 and bb21217 if all three therapies eventually win FDA approval.

Now what

Estimates peg the growing multiple myeloma treatment market to be worth $27 billion by 2022, suggesting there's a lot at stake for developers of next-generation therapies, including AMG 420 and bb2121/bb21217. The sheer size of the market, however, could mean there's room for multiple treatment approaches, particularly since existing therapies and those under development aren't cures, and thus, many patients may not respond to them or may see their disease relapse following these treatments.

Amgen and bluebird bio's data is relatively limited for these therapies, so investors will want to keep tabs on results from ongoing trials that could support regulatory filings for approval. bb2121 is furthest along in this process, looking for a possible OK from the FDA in 2020. Assuming bluebird bio's bb2121 registration-enabling trial results confirm prior findings, it could be on track to be a blockbuster, making buying bluebird bio stock following its drop in December intriguing.

Todd Campbell owns shares of Amgen, Bluebird Bio, and Celgene. His clients may have positions in the companies mentioned. The Motley Fool owns shares of and recommends Bluebird Bio and Celgene. The Motley Fool recommends Amgen. The Motley Fool has a disclosure policy.