Results from clinical trials in patients with advanced melanoma highlighted the ongoing rivalry between best-selling cancer immunotherapies Keytruda and Opdivo — from Merck & Co. Inc. and Bristol-Myers Squibb Co., respectively — at the 2019 annual meeting of the American Society of Clinical Oncology on June 3.

Both Keytruda and Opdivo are checkpoint inhibitors. They work by spurring the immune system to shrink tumors by blocking a signaling pathway between the cancer cells and immune cells. More and more, the treatments are being combined with other cancer drugs to maximize their effectiveness.

The two companies have various approvals for different types of cancer, but both began with U.S. nods in advanced melanoma in 2014.

Longevity of Opdivo and Yervoy

Bristol-Myers announced long-term analyses of two studies in which melanoma patients received a combination of Opdivo and the company's other cancer drug Yervoy.

In a five-year analysis of what began as an early-stage trial, Bristol-Myers found that 57% of patients receiving the combination were alive for four years or longer. The trial included patients who had been treated and untreated prior to the Opdivo-Yervoy regimen.

For patients who discontinued treatment, 56% lived for three years.

In a separate, long-term phase 3 study called Checkmate-067, Bristol-Myers found that patients reported stable quality of life from the beginning of treatment, which was maintained during and after follow-up. More than 945 patients were enrolled in that trial.

"These latest results provide further support for the long-term scientific rationale for combining Opdivo and Yervoy for the treatment of advanced melanoma," said Arvin Yang, Bristol-Myers' development lead for melanoma and genitourinary cancers, in a release. "We will continue to evaluate the combination in these patients, as it provides us with a wealth of valuable scientific information on the impact of immuno-oncology therapy in this population."

Keytruda and Dynavax

In another case of immunotherapy mix-and-match, Merck has teamed up with Dynavax Technologies Corp. to combine Keytruda with the Berkeley, Calif.-based company's experimental SD-101 for patients with advanced melanoma.

SD-101 is a therapy that makes use of a different cell signaling pathway but, like other immunotherapies, also kick-starts the immune system to fight cancer.

In the phase 2 study results announced at the ASCO meeting, the companies found that 72% of patients receiving the combination lived for 18 months without their disease getting worse. The companies will continue to gather data from the study, they said in a release.

"To consistently see an overall response rate above 70% among advanced melanoma patients, which has historically been a difficult population to treat, is very encouraging and exciting," Dynavax Chief Medical Officer Robert Janssen said.

Furthermore, the combination was able to target tumors that are normally a challenge for immunotherapies. These tumors, called "cold," are not inflamed and do not contain as many immune cells in their vicinity. The Keytruda and SD-101 combination was able to convert cold tumors into hot ones, according to the release.

No side effects were found in addition to those from Keytruda alone.

The 2019 American Society of Clinical Oncology meeting is expected to bring together more than 32,000 professionals from around the world, with more than 2,400 study abstracts to be presented on-site and an additional 3,200 abstracts to be published online.