A former protege of legendary Fidelity investor Peter Lynch has large positions in Alphabet Inc. (GOOGL), Facebook Inc. (FB) and Blackstone Group LP (BX), but says three other stocks are poised to soar as they dominate their respective markets.  according to Barron's. After working at Fidelity for more than 20 years, Karen Firestone founded Aureus Asset Management, which has returned more than 10% a year over the last decade. 

In a recent interview with Barron's, she singled out three stocks in particular for their strong prospects. 

PayPal: Ripe With Potential

Payment processing giant PayPal Holdings Inc. (PYPL)'s stock is up nearly 80% year-to-date (YTD) at the time of report, Google Finance data shows. The company's potential market is $100 trillion, Firestone told Barron's. This figure dwarfs the company's current market capitalization, which was $85 billion at the time of report. (For more, see also: Samsung Pay Partners with PayPal.)

CME Group: Grabbing Market Share

Exchange operator CME Group Inc (CME)'s shares have risen 16% YTD. CME Group, which offers a wide range of financial products, has been building its market share as trading volume grows, Firestone claimed. She asserted that this company's stock, which has been trading north of $130, has a true value of $165 or $170. 

HealthEquity: $1 Trillion Market

HealthEquity Inc. (HQY), the leading provider of Health Savings Accounts (HSAs), has risen roughly 20% YTD. However, its shares could experience significant upside as its market grows, Firestone told Barron's. While the market for HSAs is worth less than $40 billion right now, it could expand to $1 trillion over time, she said. Since HealthEquity has close to 20% of this market right now, the total value of its HSAs could potentially skyrocket. (For more, see also: Pros And Cons of a Health Savings Account.)

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