A small drug company that's trying to make cancer treatments safer just received a huge endorsement

CytomX, a biotech that's developing safer ways to administer cancer immunotherapies, just got another $200 million from drug giant Bristol-Myers Squibb.

Bristol-Myers has two drugs, Opdivo and Yervoy, that are a part of a new class of cancer treatments called cancer immunotherapy that harness the body's immune system to go after cancer. Specifically, they're a type of immunotherapy called checkpoint inhibitors. These checkpoint inhibitors take the foot off the brake pedal in the immune system, unleashing the immune system on the cancer.

But just like chemotherapy and radiation, immunotherapy can have side effects. Those checkpoint inhibitors act as "checkpoints" for a reason. In a normal body, they keep the immune system from going after healthy cells. So manipulating them, while it might help kill cancer cells, can at times be a blunt instrument. The newly freed immune system can, in some cases, start attacking healthy organs in the body.

What CytomX is trying to do is activate the drug only when it's by diseased tissue, using something called "Probodies." That way, it might be possible to reduce some of the side effects that current cancer immunotherapy treatments have.

"CytomX's Probody platform has enhanced our discovery research as we seek to direct the therapeutic effects of immunotherapy in a more targeted approach against tumors," Carl Decicco, head of discovery at Bristol-Myers, said in a news release.

CytomX originally partnered with Bristol-Myers back in 2014 and also has partnerships with drug giants AbbVie and Pfizer.

The partnership is worth up to $3.8 billion, factoring in roughly $3.6 billion in potential milestone payments. CytomX's stock was up 24% Monday morning.