Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

The Dow Jones Industrial Average (DJINDICES:^DJI) has made history again during its spectacular run-up in 2013, this time crossing the 16,000-point mark during Monday trading. The blue-chip index has flirted with the mark all day, and as of 2:30 p.m. EST, the Dow has gained more than 60 points. Financial and industrial stocks are leading the push higher on a day when most of the index has moved into the green.

Out of health care, Merck (NYSE:MRK) has lost around 0.04% despite promising data data for one of its developmental cancer-fighting drugs. Let's catch up on what you need to know.

A new hope for Merck
Merck's PD-1 inhibitor MK-3475, which the company hopes will eventually add to its oncology portfolio in fighting multiple types of cancer, showed strong promise in clinical trials by keeping more than 80% of advanced melanoma patients alive after a year. That's a far better result than usual survival rates for the disease, and it has Merck hopeful that MK-3475 can pick up the pace in the company's lackluster pipeline, which is in need of some hits after disappointing lately.

MK-3475 could be a big winner for Merck if it shows similar strong results for other cancer types -- and gets by regulators, too. Some analysts have pegged the drug at garnering peak sales of up to $500 million in treating melanoma alone. By adding more cancer treatment indications, the drug could hit blockbuster status and potentially see up to $3 billion in peak sales, according to some projections.

That'd be a huge win for Merck's anti-cancer portfolio, which has seen current top seller Temodar lose nearly 14% in sales through the first nine months of the year.

However, MK-3475 and Merck aren't without competition. Rival Bristol-Myers Squibb (NYSE:BMY) is testing a similar PD-1 inhibitor, nivolumab, both on its own and in combination with the company's cancer-fighting therapy Yervoy. Nivolumab could be huge for Bristol: Some analysts have said that the drug could garner up to $4 billion in peak sales, although that's on the high range of estimates. Yervoy's already been a big hit for Bristol, with 41% sales growth through the first nine months of the year putting the drug near or on blockbuster pace for all of 2013

Even with competition, Merck's drug looks strong so far. If Merck can gain similar results in other cancers as it has with melanoma, MK-3475 could become the next big addition to this Big Pharma giant's portfolio.