Healthcare stocks are hot this year. The sector-tracking iShares S&P Global Healthcare index has already tacked on a 17% gain this year.

If you're looking to catch a ride on the healthcare train, Align Technology, Inc. (NASDAQ:ALGN), Mazor Robotics Ltd. (NASDAQ:MZOR), and Progenics Pharmaceuticals Inc. (NASDAQ:PGNX) are great places to start. Here's why.

Three doctors making thumbs up gesture.

Image source: Getty Images.

Smiles for your portfolio

Thanks to Align Technology and its nearly invisible dental aligners, clunky metal braces are becoming a thing of the past. This company was an early adopter of the 3D technology that underpins its products, and patent protection allowed Align's Invisalign brand aligners to disrupt a multibillion-dollar market for adult braces practically free of any competitors.

Although Align's success is attracting competition, a full-steam-ahead approach to increasing exposure for Invisalign has made it the only brand of dental aligners patients actually ask for. In the second quarter, the company trained nearly 5,000 new doctors to use Invisalign, and the teen segment is just beginning to surge. Now that the company has trained over 100,000 doctors, started treating over 1 million teenagers, and begun manufacturing products in the enormous Chinese market, there's plenty of room to grow.

Align generated 27.3% more revenue last year than the year before, and it looks as if surging teen and international segments are accelerating growth. Second-quarter sales jumped 32.3% over the same period last year to $356.5 million.

Align's blazing-fast growth hasn't gone unnoticed. This top-performing healthcare stock has already risen about 92% this year and at recent prices trades for about 54 times this year's earnings estimates. It might be best to wait for a pullback, as any hint of a slowdown could send the price tumbling from its dizzying height at the moment.

Doctor showing a chest x-ray.

Image source: Getty Images.

Sending tingles down your spine 

Mazor Robotics builds robotic surgical systems that assist surgeons during routine spine and brain procedures. Laser-guided precision allows surgeons to make smaller incisions than a human hand. Minimally invasive surgery results in shorter recoveries and fewer complications, which is music to hospital administrators' ears.

Demand for Mazor's surgical systems drove second-quarter revenue 87% higher than the same period last year. At just $15.5 million during the three-month period ended June, though, there's lots of room to continue growing at a mind-boggling pace. The company expects the total market for robotic spinal procedures to pass $2.77 billion by 2022.

The world's largest medical-device manufacturer, Medtronic, has a large presence in the spinal repair market and an 11.9% equity stake in Mazor Robotics. Medtronic's enormous sales force will be responsible for marketing Mazor's latest robotic surgical system, along with the consumable instruments that must be replaced after each procedure. I don't think there's a hospital on Earth that doesn't have a relationship with Medtronic, and I wouldn't be surprised if the partnership helps Mazor maintain a blazing-fast growth rate for years to come.

A biotech bargain

Progenics Pharmaceuticals Inc. boasts a commercial-stage drug, Relistor, for patients with opioid-induced constipation, plus two compounds in late-stage development, 1404 and Azedra. A slower-than-expected launch for a more convenient tablet form of Relistor and an application filing delay for Azedra has pressured this biotech stock's market cap down to a sprightly enterprise value of just $383 million at recent prices.

Although Valeant probably won't achieve more than $1 billion in annual Relistor sales as the company previously predicted when licensing rights to the drug from Progenics, a high-margin revenue stream will help fund development of 1404 and Azedra, both wholly owned programs. Azedra is an experimental treatment for pheochromocytoma and paraganglioma, two ultra-rare malignancies that affect adrenal glands. Clinical trial data supporting a new drug application is positive enough to suggest a likely approval, but the company has delayed completing the submission to prepare the proposed manufacturing site for an FDA inspection.

Manufacturing site concerns have derailed more than a few high-profile applications recently, so I'm inclined to view Progenics' caution in a positive light. If approved, annual Azedra sales are expected to top out around $250 million, and 1404 could be even more successful. The company's experimental imaging agent presents a vast improvement over current methods of non-invasive prostate cancer detection, and the company is currently running a late-stage clinical trial designed to support an application.

I'd say 1404 and Azedra each look promising enough to justify this stock's recent price on their own. Add in a modest royalty stream from future Relistor sales, and it looks as if Progenics is one of the most underappreciated healthcare stocks you can buy right now.

Cory Renauer owns shares of Medtronic. The Motley Fool owns shares of and recommends Align Technology and Valeant Pharmaceuticals. The Motley Fool owns shares of Medtronic. The Motley Fool has a disclosure policy.