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CHICAGO (TheStreet) -- Combination therapy involving two immunotherapy drugs from Bristol-Myers Squibb (BMY) extended median overall survival to almost three and half years in patients with advanced melanoma, according to updated results from a phase I study described as "remarkable" by investigators at the American Society of Clinical Oncology (ASCO) annual meeting. 

The two Bristol drugs -- the still-experimental nivolumab and the approved Yervoy -- work by blocking "checkpoints" on T-cells which prevent the immune system from recognizing and killing cancer cells. Similar checkpoint inhibitors, or anti-PD1 and anti-PDL-1 drugs, are being developed by Merck (MRK) and AstraZeneca (AZN) , among other companies. Collectively, the development and approval of new classes of cancer immunotherapies have the potential to generate tens of billions of dollars in new revenue for these companies. 

In the study, 94 melanoma patients no longer responding to prior therapies -- half with very advanced disease -- all received combinations of nivolumab and Yervoy at different doses. Long-term follow-up results from 53 patients enrolled in the first four dosing cohorts were announced Monday. Overall 22 of the 53 patients (41%) responded to the nivolumab-Yervoy combination therapy. Across all doses, the one- and two-year survival rates were 85% and 79%, respectively, with a median overall survival of 39.7 months.

"Just a few years ago, median survival for patients diagnosed with advanced melanoma was as little as a year or less, and only approximately 20-25% survived two years, so it's truly remarkable that we're seeing a median survival over three years in this trial," said Dr. Mario Sznol from Yale's School of Medicine and an investigator in the study, in a statement.

Sznol notes that median survival in melanoma is about 16-18 months when cancer immunotherapies are used alone, so the combination of two of these new drugs doubled survival. He cautions, however, that the phase I study was small so encouraging results need to be confirmed in a larger, randomized phase III study.

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Bristol is conducting a 900-patient, phase III study in melanoma comparing nivolumab monotherapy, the nivolumab-Yervoy combination and Yervoy monotherapy. At the nivolumab-Yervoy dose being used in the phase III study, the one- and two-year overall survival rates were 94% and 88%, respectively, in the phase I study. 

Also today, Merck announced results from a study of its checkpoint inhibitor MK-3475 used as monotherapy in melanoma patients. Overall, 34% of patients experienced a tumor response with a one-year survival rate of 69%. In a subgroup of patients not previously treated with Yervoy, the response rate to MK-3475 was 40% and the one-year survival rate was 74%.

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;

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