Image source: Merck.

You wouldn't know it from Merck's (NYSE:MRK) stock performance in 2015 -- it's down 8% year to date -- but it's actually had a pretty good year.

Merck has successfully put its growth issues tied to the patent loss of blockbuster asthma drug Singulair, once a $5 billion global drug, safely in the rearview mirror, and has managed to modestly grow its sales on an operating basis in each quarter this year once adverse currency effects are removed from the equation.

Beyond just its earnings reports, Merck has also announced a number of headlines that support a healthy long-term growth outlook. Let's briefly take a look at Merck's best headlines in 2015, in no particular order, and examine why these stories offer so much promise.

Expanded use is a good thing
Arguably the biggest headline for Merck in 2015 was the announcement in early October that the Food and Drug Administration had approved its cancer immunotherapy drug Keytruda as a treatment for advanced non-small cell lung cancer patients who express high levels of PD-L1.

Image source: Bristol-Myers Squibb.

Keytruda was first approved in September 2014 as a treatment for BRAF V600 mutation-positive metastatic melanoma, with its competitor Opdivo, developed by Bristol Myers-Squibb (NYSE:BMY), also getting the nod in metastatic melanoma a short time later. However, Bristol-Myers Squibb's Opdivo was approved to treat advanced NSCLC cases months before Keytruda, so this expansion is viewed as critical to allowing Keytruda to actively garner advanced NSCLC market share from traditional competitors and possibly Opdivo.

What makes Keytruda such an intriguing treatment is that it's designed to enhance the body's immune system to better locate and fight cancer. Cancer is such an effective disease because it often goes undetected by the immune system. Checkpoint inhibitors such as Merck's Keytruda and Bristol-Myers' Opdivo turn off that immunosuppressant quality and expose cancer to the immune system. In clinical studies, both drugs delivered overall response rates in advanced NSCLC patients with high PD-L1 expression of around 60%. For added context, the typical response rate for metastatic NSCLC is usually around 25%, so this is big news.

Image source: Merck.

Jimmy Carter gets a clean bill of health
Along the same lines as the label expansion, earlier this month former President Jimmy Carter announced that he was cancer free after taking Keytruda. Carter's metastatic melanoma led to spots on his liver as well as four small lesions on his brain, but following treatment with Keytruda Carter announced that he was cancer-free. He was still undergoing treatment at the time of the announcement.

This announcement vindicates the effectiveness of cancer immunotherapies by suggesting they have the potential to treat multiple forms of solid tumors, and potentially even cancers of the blood. This is also why Merck is currently studying Keytruda in around 30 clinical studies as a monotherapy and combination therapy.

During the third quarter, Merck's management team noted that the company maintained a 70% market share on high-PDL1-expressing metastatic melanoma patients, and following Carter's success, I could possibly see this share moving even higher.

A hepatitis C approval is within sight
One of the more exciting developments in 2015 was Merck's filing for the marketing approval of its hepatitis C combination therapy consisting of grazoprevir and elbasvir in May. This once-daily cocktail drug will directly compete against Gilead Sciences' (NASDAQ:GILD) Harvoni in genotype 1, although Merck is seeking to gain approval in genotypes 1, 4, and 6.

Image source: Gilead Sciences.

Up until now, Gilead Sciences has dominated the hepatitis C treatment scene because it's the only company to offer a once-daily pill, and its efficacy has been practically unmatched. However, Merck's combo therapy produced sustained virologic responses that were in the upper 90-percentile in clinical studies, which means Gilead's Harvoni could face some stiff competition in the coming months depending on how Merck prices and launches its drug (if approved).

Also exciting, Merck has a three-compound cocktail drug in clinical trials that could really put some fear in Gilead. The combo of grazoprevir, MK-3682, and a new version of elbasvir known as MK-8408, delivered a cure rate of 91% over eight weeks in genotypes 1, 2, and 3 patients in a phase 2 study. If Merck can shorten the treatment timeframe to successfully treat HCV patients, it could unseat Gilead Sciences as the dominant player. There are an estimated 180 million people worldwide with hepatitis C, so this could be a huge long-tail growth opportunity for Merck.

Merck boosts its dividend
Lastly, Merck announced in November that it was boosting its quarterly dividend by $0.01 to $0.46 per quarter. Raising its dividend by a penny may not seem worthy of breaking out the champagne, but, considering its recent patent woe issues, Merck's commitment to growing its dividend should be viewed as confirmation that the tide is turning.

Inclusive of its raise, shareholders are now set to receive a 3.5% yield, which is substantially higher than the average yield of the S&P 500, which is around 2%.

Should its dividend raise and other top headlines from Merck get you excited about its future? I think so, considering that Merck has witnessed strong early growth from Keytruda and it could soon add a blockbuster HCV drug to its product portfolio. Merck's growth rate certainly isn't going to knock anyone's socks off, nor should investors expect anything more than modest share price appreciation out of this Big Pharma giant. But its superior dividend and relatively predictable cash flow make it a potentially attractive investment for retirees and buy-and-hold investors with a low tolerance for risk.