Reaching your retirement savings goal isn't easy, but your chances of meeting or exceeding your expectations improve if you invest in stocks over the long term.

Although the stock market may be volatile at times, company valuations tend to increase in the long run. We've witnessed 35 separate declines of 10% or more in the broad-based S&P 500 since 1950. Yet every single one of these corrections -- some nearly as steep as 60% -- has been completely wiped out by bull market rallies. Sometimes it takes weeks or months, and occasionally years, but the stock market always seems to put bear markets firmly in the rearview mirror.

For investors with a lot of time on their hands to invest, like millennials, that's a pretty dependable formula for success.

Cutting-edge healthcare stocks for millennials to consider buying

The big question, then, becomes what stocks to buy. For millennials, who generally have three or four decades left in the labor force before retiring, I'd suggest taking a much closer look at the following three healthcare companies, which just so happen to have cutting-edge products that are transforming the treatment landscape.

Bristol-Myers Squibb

There are well over 300 publicly traded drug-developers for investors to choose from in the healthcare space, but few are making waves as big as U.S. pharmaceutical giant Bristol-Myers Squibb (NYSE:BMY).

What makes Bristol-Myers such an intriguing company for millennials is that it's on the cutting edge of two major health concerns: cancer and blood clotting.

Image source: Bristol-Myers Squibb

Without question, the star of the show is cancer immunotherapy Opdivo, which is a PD-1 inhibitor. In simple-to-understand terms, the reason cancer proliferates within our bodies is because our immune system can't detect it. Cancer immunotherapies like Opdivo block the pathway that cancer cells use to avoid detection, thus exposing them to the immune system and allowing the immune system to attack. The idea of using the patient's own immune system to fight cancer isn't new, but Bristol-Myers is among the first to have a working product.

Opdivo is currently approved to treat certain types of melanoma, lung cancer, and kidney cancer. It's also involved in dozens of combination studies across a few dozen tumor types. Needless to say, there are ample opportunities for Opdivo to expand its uses going forward -- and make an honest run at $10 billion in peak annual sales. For context, it's probably on pace for around $3 billion in sales in 2016 after turning in $704 million in sales in Q1.

Image source: Bristol-Myers Squibb.

Bristol-Myers, in collaboration with Pfizer (NYSE:PFE), also has blood-thinning medication Eliquis, which is on pace for about $3 billion in sales itself in 2016. In a head-to-head, double-blind study against longtime standard-of-care Warfarin, Bristol-Myers' and Pfizer's Eliquis blew its competitor out of the water. The Eliquis arm exhibited fewer strokes or system embolisms, less major bleeding, fewer hemorrhagic strokes, and, most importantly, fewer deaths during trial. Eliquis could easily see its label expand as it becomes the new standard among oral anticoagulants.

After producing $2.01 in full-year EPS for 2015, Bristol-Myers is on pace for $4.58 in full-year EPS by 2019. It's a cutting-edge drugmaker that millennials should seriously consider buying.

Intuitive Surgical

Nothing says cutting-edge like robots, and that's exactly what robotic surgical company Intuitive Surgical (NASDAQ:ISRG) brings to the table (pun fully intended).

Intuitive Surgical's cutting-edge product is its line of da Vinci surgical robotics, which are designed to help physicians perform certain surgical procedures. Since the company was founded 21 years ago, more than 3 million procedures have been performed using its robotic technology, and as of the second quarter of 2016, 3,660 da Vinci surgical systems were installed around the world (two-thirds in the U.S.). At the moment, its surgical robotics account for more than 80% of prostate cancer and malignant hysterectomy surgeries, and the company is angling to grow its sub-10% market share in the colorectal, ventral hernia, and thoracic surgery markets in the coming years.

Image source: Intuitive Surgical.

Intuitive Surgical has a number of advantages that put it in a prime position to succeed over the long-term. For starters, it has had two decades to build its network of installed da Vinci products. It takes time to train physicians to use its machines, which means any competitor looking to introduce its own robotic surgical system will need years, or even decades, to make its network even remotely comparable to what Intuitive Surgical currently offers.

Another advantage is the high-margin services that Intuitive Surgical offers. The da Vinci surgical system isn't cheap, with an average selling price of $1.54 million apiece. However, each machine brings in annual revenue of $138,000, at least based on 2015 data. This is because of the training and regular servicing Intuitive Surgical's robotic system needs, on top of the revenue the company can earn from procedures performed. In a way, you could say that Intuitive Surgical has introduced its own razor-and-blades model within the medical landscape. 

With a niche offering and little in the way of viable competition, this cutting-edge robotics giant could be worth a look by millennials.

Myriad Genetics

Lastly, don't forget about diagnostic companies and the role they're playing in personalizing treatment, especially when it comes to cancer. This is why a diagnostic giant like Myriad Genetics (NASDAQ:MYGN) makes the list of cutting-edge healthcare stocks worth millenials' consideration.

The idea behind personalized medicine is pretty straightforward: We're all different, so why should we accept one-size-fits-all medical treatments? Molecular diagnostic companies like Myriad Genetics look for specific genes or biomarkers that help physicians identify what unique qualities you have so they can give you the best chance of fighting (and beating) your disease. For instance, Merck's cancer immunotherapy Keytruda works best in advanced non-small-cell lung cancer patients with high levels of PD-L1-expression; identifying this specific malady can help the physician prescribe the medication that gives the patient his or her best chance of success/survival.

Myriad Genetics' bread-and-butter diagnostic tool is BRACAnalysis, a test for women to see whether they carry the mutant BRCA1 or BRCA2 genes. These two genes are known to increase the risk of developing breast and/or ovarian cancer. BRACAnalysis received acclaim after actress Angelina Jolie tested positive for one of these mutations and voluntarily chose to undergo a mastectomy. Having witnessed her mother die of breast cancer at a relatively young age, Jolie wished to take precautions to ensure she'd live a long life for her children.

But it's not just this single gene test that's exciting the medical community and investors alike. Myriad Genetics also offers Prolaris and Vectra DA. Prolaris is a molecular test that helps gauge the aggressiveness of prostate cancer tumors so physicians have a better idea of which medicine to use to fight the disease. Meanwhile, Vectra DA is an advanced blood test that, in combination with physical exams, can help rheumatoid arthritis patients identify their risk of future joint damage.

Myriad finds itself on the cutting edge of personalized medicine, and that's a good place to be if you're a long-term investor looking for great stocks to buy.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.