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CHICAGO (TheStreet) -- Merck's (MRK) is already in the FDA review process for its checkpoint inhibitor MK-3475 as a treatment against advanced melanoma. New MK-3475 melanoma data released today for the first time bolster the arguments for the drug's approval.

MK-3475 belongs to a new class of drugs designed to block a cloaking mechanism used by cancer cells to hide from a patient's immune system. Similar anti-PD-1 and anti-PDL-1 drugs are being developed most notably by Bristol-Myers Squibb (BMY) , Roche (RHHBY) and AstraZeneca (AZN)  -- and all are generating a lot of attention and excitement at this year's American Society of Clinical Oncology (ASCO) annual meeting. Collectively, development and approval of these new classes of cancer immunotherapies have the potential to generate tens of billions of dollars in new revenue for the companies.

In a phase I study of 411 melanoma patients -- the largest phase I cancer study ever conducted -- treatment with Merck's MK-3475 yielded a one-year survival rate of 69%. Median overall survival has not yet been reached. Overall, 34% of patients in the study experienced tumor shrinkage. Responses were durable, with 88% still ongoing at the time of the data analysis. 

"These are early data, but they tell us that we are onto something really important," said Dr. Antoni Ribas of the David Geffen School of Medicine at UCLA and an investigator in the MK-3475 study, in a statement. 

Of the 411 melanoma patients enrolled in the study, a bit more than half had been treated previously with Bristol's Yervoy. In these patients with more advanced, progressive disease, the overall response rate to MK-3475 was 28% and the one-year survival rate was 65%. Median progression-free survival was 23 weeks. 

Merck's is seeking FDA approval for MK-3475 to treat patients with melanoma no longer responsive to Yervoy. The FDA has already granted a Breakthrough Therapy Designation to MK-3475 and the expected approval decision date is Oct. 28. 

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The remaining patients in the study were not previously treated with Yervoy. In this group, the overall response rate to MK-3475 was 40% with a one-year survival rate of 74%.

The phase I study was not randomized, meaning all patients received MK-3475. Merck is conducting additional, randomized studies of MK-3475 in melanoma and other solid tumors, including lung cancer. 

The clinical activity of MK-3475 monotherapy in melanoma appears to be very similar to Bristol's competing checkpoint inhibitor nivolumab. In an update to an ongoing study also being presented at this year's ASCO meeting, melanoma patients with no prior Yervoy experience were treated with nivolumab. The overall response rate to nivolumab was 32%, with one-, two- and three-year survival rates of 63%, 48% and 41%.

A separate, smaller study combining Bristol's nivolumab and Yervoy, also released this morning at the ASCO annual meeting, reported a median overall survival of almost three and a half years in patients with advanced melanoma.

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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