Innovation drives progress, and in the healthcare sector, that often means saving lives by finding new ways to diagnose or treat potentially deadly illnesses. Those companies at the forefront of innovation can help improve the lives of thousands of people while providing outsized returns to investors over the long run.

There are many such corporations to consider on the market, but let's examine two: Guardant Health (GH 1.90%) and Sarepta Therapeutics (SRPT -0.80%). Read on to find out why both companies are worth holding onto for a while. 

1. Guardant Health

Progress in cancer research is always important as cancer is a leading cause of death worldwide. Guardant Health focuses on developing liquid biopsies -- tests that help detect signs of cancer from blood samples. This cancer testing method is often preferred to tissue biopsies since the former are non-invasive and faster.

Guardant Health's products have a range of applications, such as helping physicians choose the best treatment course for cancer patients, estimating the probability of recurrence in early-stage patients, and helping biopharmaceutical companies pick suitable candidates for their oncology-related clinical studies.

Guardant Health can grow in prominence in the years ahead while its stock price appreciates for at least three reasons. First, it continues to develop newer products. And there is plenty more work to be done. For example, the company is running a clinical trial to test its Shield blood test in detecting colorectal cancer early.

In August, it received approval from the U.S. Food and Drug Administration (FDA) for its Guardant 360CDx test in helping oncologists figure out which patients can most benefit from Enhertu, a cancer medicine marketed by AstraZeneca.

Second, some of Guardant Health's products will be able to reach more customers as third-party payers get on board. In August, the company's Guardant Reveal test -- which helps with cancer residual and recurrence monitoring -- earned Medicare coverage.

Third, Guardant Health still has a massive addressable market ahead, which it estimates at more than $80 billion. The company reported $117.4 million in revenue in the third quarter, representing a 24% year-over-year increase. Naturally, there are some risks associated with this company, including the fact that it isn't profitable yet, which partly explains its poor stock market performance lately. 

Guardant Health reported a net loss per share of $1.58 in the period, much worse than the net loss per share of $1.06 recorded in the third quarter of the previous year. For investors in it for the long term, Guardant Health is worth it as the company keeps developing innovative products that allow us to fight against cancer better.

In 10 years, the red ink the company is currently showing on the bottom line will mean little.

2. Sarepta Therapeutics 

Developing medicines for rare diseases is challenging because it is sometimes seen as an unprofitable venture -- or at least one not very likely to be profitable over the long run. But that's not stopping Sarepta Therapeutics, a biotech that focuses on rare illnesses, especially one by the name of Duchenne muscular dystrophy (DMD).

This genetic condition weakens patients' muscles. It is a progressive disorder that is typically fatal. But Sarepta Therapeutics has made tremendous progress in this area. The drugmaker earned FDA approval for its first DMD medicine -- the first ever to be granted the green light by the regulatory agency -- back in 2016.

Since then, Sarepta Therapeutics has expanded its lineup with a couple more DMD treatments. Next year, it could earn yet another one. According to some estimates, about 20,000 children are diagnosed with DMD every year. While that's not a lot, Sarepta Therapeutics currently markets the only FDA-approved drugs for this condition.

Being the only game in town counts for a lot. And the company's pipeline has other candidates targeting this illness. Sarepta Therapeutics is also going after other rare diseases and currently boasts more than 40 clinical programs. The biotech's financial results aren't excellent yet, mostly due to the bottom line.

In the third quarter, it reported revenue of $230.3 million, 21.6% higher than the prior-year quarter. The drugmaker's net loss per share worsened to $2.94, down from the $0.60 net loss per share recorded in the prior-year quarter. But Sarepta Therapeutics' progress in helping treat DMD, and its multiple clinical programs, make it a highly promising and intriguing long-term prospect.

That's why the company's shares have outperformed the broader market this year, and they could continue delivering solid returns for a while.

Playing the long game 

Guardant Health and Sarepta Therapeutics won't make anyone rich overnight. But both healthcare companies are driving innovation in their respective fields, which is a major reason they could handsomely reward shareholders down the line. Although the fact that neither is consistently profitable is a definite downside, the potential upside outweighs the risks, at least in my view. Investors should strongly consider adding both to their portfolios.