Patience is a virtue, or so says an old proverb. That sentiment certainly applies to the stock market. The longer one holds shares of great companies, the greater the potential for compounding to work its magic. That's why the buy and hold strategy works. However, it can be tough to find quality stocks worth holding onto.

If you need some inspiration, here are two cancer-focused companies that could provide excellent returns in the coming years: Exact Sciences (EXAS -3.97%) and Guardant Health (GH -3.60%). Although both companies have lagged the market recently, they boast substantial upside potential if we go by price targets set by Wall Street analysts. Here's the rundown. 

EXAS Chart

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1. Exact Sciences

Shares of Exact Sciences could skyrocket by 102% if it lives up to its average price target of $94.18, according to Yahoo! Finance. Can the company pull it off? To answer that question, let's look into the company's business. Exact Sciences focuses on developing and marketing products to detect early-stage colorectal cancer.

Catching this potentially deadly disease as early as possible can determine the likelihood that the patient will live. That's why Exact Sciences' products are important for patients and healthcare providers. The company's crown jewel is a test for colorectal cancer called Cologuard. Colorectal cancer is highly treatable when caught early, yet it remains the second leading cause of cancer death.

Regular screenings are recommended for those 45 years and older who are at average risk of this type of cancer. But according to Exact Sciences, 46 million people in the U.S. remain unscreened. The company sees an $18 billion opportunity in this market. Exact Sciences reported revenue of $486.6 million in the first quarter, 21% higher than the comparable period of the previous fiscal year.

Exact Sciences is working on the second generation of Cologuard, which, among other things, will decrease false-positive rates. The company still has considerable room to grow in the colorectal cancer-screening market even if it doesn't capture all of it. 

One worry with Exact Sciences is that it remains unprofitable. The company's net loss per share in the first quarter came in at $1.04 compared to a net loss per share of $0.18 reported in the first quarter of 2021. Widening net losses are never a good sign, especially with slowing top-line growth. Those factors explain Exact Sciences' recent poor performances on the stock market -- besides marketwide economic worries. 

But it's also worth mentioning that Exact Sciences boasts other opportunities. It is currently working on a multi-cancer early detection test. Exact Sciences sees a $25 billion opportunity in multi-cancer screening. The company's overall addressable market should help it grow its revenue in the coming years and eventually turn green on the bottom line.

However, the Street's price target seems well out of range for the company within the next 12 months. There is too much uncertainty surrounding the economy, and until equity markets recover, it will be challenging to convince investors to turn to unprofitable companies like Exact Sciences.

Still, for long-term investors looking to take advantage of current market conditions, Exact Sciences could be worth serious consideration.

2. Guardant Health 

Guardant Health describes itself as a precision oncology company. It specializes in liquid biopsies, tests that allow physicians to detect cancer cells from blood samples. Liquid biopsies are faster and a lot less invasive than tissue biopsies. That's why many patients might prefer those options. Guardant Health's products include GuardantOMNI and Guardant360.

Drugmakers use the former to help identify patients with the right molecular profile to include in their clinical trials. GuardantOMNI helps speed up the clinical trial process and increase the probability of success. The Guardant360 tests help predict whether patients will respond to targeted cancer therapy. Guardant Health is working on developing other products as well.

For instance, there is Guardant SHIELD, a liquid biopsy test for the early detection of several cancers, including lung and colorectal cancer. Guardant Health sees an addressable market north of $80 billion across the entire range of the products it offers (or is currently developing).

The company reported $96.1 million in revenue in the first quarter, representing a 22% year-over-year increase. Having barely scratched the surface of its market, Guardant Health boasts fantastic growth opportunities ahead.

On the downside, Guardant Health isn't profitable either. The company reported a net loss of $123.2 million in the first quarter compared to a net loss of $109.7 million recorded in the first quarter of 2021. This factor might make the company a volatile pick in the short run, especially given the current state of the market.

That's one reason it'll be difficult for Guardant Health to match Wall Street's predicted upside of 133% as of this writing. Still, the company's portfolio of life-saving products, coupled with growing revenue and a massive market opportunity, help somewhat make up for these risks, in my view.

For patient investors, Guardant Health is worth holding through these turbulent times.