Profitability isn't a prerequisite for impressive stock performance. This was definitely demonstrated over the past week. Three of the biggest gains came from companies in the healthcare sector that are nowhere close to turning a profit.

Tandem Diabetes Care (NASDAQ:TNDM), TransEnterix (NYSEMKT:TRXC), and CRISPR Therapeutics (NASDAQ:CRSP) ranked among the biggest healthcare winners for the week. What drove these stocks higher -- and are they still buys? Here's what you need to know about these hot healthcare stocks. 

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1. Tandem Diabetes Care

Tandem Diabetes Care stock skyrocketed 44% this week. The medical device stock received a big boost from an analyst upgrade on Monday, with the positive momentum carrying over through the rest of the week.

Piper Jaffray analyst J.P. McKim upgraded Tandem Diabetes Care stock from neutral to overweight. He also bumped his one-year price target for the stock from $8 per share to $13. Tandem stock began the week higher than McKim's prior target. Thanks to the big jump this week, the share price is now only 6% below the new one-year price target. 

Why such bullishness about Tandem? The company has a product on the way that it thinks could leapfrog its competitors. Tandem hopes to launch a "closed loop" system in the first half of 2019 that monitors blood glucose levels in patients and uses an algorithm to dose them with insulin when needed. McKim believes this new system could enable Tandem to rapidly gain market share in the booming diabetes-care market.

2. TransEnterix

TransEnterix stock vaulted nearly 44% higher this week. The catalyst for the surgical robot developer actually originated in the previous week, when the company announced its first-quarter results.

The highlight from TransEnterix's Q1 update was that the company sold two of its Senhace robotic surgical systems. However, TransEnterix announced even better news: It's sold three more systems already in the second quarter. Five of these six sales so far in 2018 have been made outside of the U.S. 

There's a lot for customers to like about the Senhance system. It incorporates haptic feedback, which recreates the sense of touch that surgeons would feel if they were performing procedures using traditional surgical instruments instead of a robotic system. Senhance enables surgeons to control the camera mounted on the robot arms by moving his or her eyes and head. And the system's instruments are reusable, which could give Senhance a cost advantage over Intuitive Surgical's da Vinci robotic surgical system.

3. CRISPR Therapeutics

CRISPR Therapeutics stock jumped nearly 23% this week. Although there weren't any new developments for the biotech over the past few days, investors appear to still be pumped from the company's first-quarter update provided on May 8, 2018.

CRISPR Therapeutics and partner Vertex Pharmaceuticals plan to begin a phase 1/2 clinical study in the second half of this year to evaluate gene-editing therapy CTX001 in treating transfusion-dependent beta-thalassemia, a rare genetic blood disorder. The two companies also expect to initiate a clinical study of CTX001 in treating sickle cell disease later in 2018.

CTX001 isn't the only program in the hopper for CRISPR Therapeutics, though. The biotech intends to file for FDA approval by the end of the year to begin clinical studies for CTX101, its lead allogeneic CAR-T cell therapy. CRISPR Therapeutics presented encouraging data for this program at the American Association for Cancer Research (AACR) annual meeting in April. 

Are they buys?

I think Tandem Diabetes Care could enjoy success with its "closed loop" system, assuming it gets a green light from the FDA. However, the company is a small fish swimming in waters with some big sharks like Medtronic. My preference is to watch Tandem from a distance.

You could make a similar argument for TransEnterix. The small company's CEO has stated that TransEnterix won't compete directly against robotic surgical systems giant Intuitive Surgical. I doubt that peaceful coexistence will last very long, though. 

My hunch is that TransEnterix will continue to see growth for its Senhance system. The problem as I see it, though, is that the growth won't be fast enough to avoid a dilution-causing stock offering in the not-too-distant future. I think TransEnterix could be a great long-term play, but I'd like to see the company get on better financial footing before thinking about buying the stock.

That leaves CRISPR Therapeutics. The biotech is also likely to have to go to the well more in the future to raise cash through stock offerings. I'm very optimistic, though, about the future of gene editing. And I like that CRISPR Therapeutics has a strong partner in Vertex -- one of my favorite biotechs on the market. There are plenty of risks for CRISPR Therapeutics, but I think it's a stock to buy for investors willing to wait patiently for several years. 

Keith Speights owns shares of Vertex Pharmaceuticals. The Motley Fool owns shares of and recommends Intuitive Surgical. The Motley Fool owns shares of CRISPR Therapeutics and Medtronic. The Motley Fool recommends Vertex Pharmaceuticals. The Motley Fool has a disclosure policy.