Biotech giant Regeneron (REGN 1.81%) and streaming specialist Roku (ROKU -1.10%) have been solid performers for most of the year, but both stocks recently jumped following their third-quarter earnings releases. While a single quarterly update rarely fundamentally changes the investment thesis of a corporation, both Regeneron and Roku had some positive developments worth reviewing, further solidifying why they are excellent stocks to buy. Let's dig in.

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1. Regeneron

Regeneron has relied on two key medicines for growth for some time now. The first is Eylea, which treats age-related macular degeneration, an eye disease. Regeneron comarkets Eylea with Bayer. The second is eczema therapy Dupixent, the rights of which it shares with Sanofi. However, Eylea has been facing competition from newly approved therapies. Thankfully, Regeneron and Bayer recently earned approval for a high-dose version of Eylea, which requires fewer doses per year without sacrificing efficacy.

This new formulation of Eylea earned approval in mid-August. It managed to generate $43 million in sales in the third quarter -- that is, in the roughly six weeks between the time it was approved and the end of September. Eylea's sales should maintain solid momentum, and that's excellent news for Regeneron and its shareholders, especially as the old version of the medicine could start facing biosimilar competition next year.

Regeneron now looks ready to take on this challenge.

Meanwhile, Dupixent is still performing exceptionally well. Its global sales in the third quarter (recorded by Sanofi) soared by 33% year over year to $3.10 billion. Regeneron's total revenue increased by 15% to $3.36 billion. The company's adjusted net income came in 5% higher than the year-ago period at $1.3 billion. Regeneron's pipeline is full of potential label expansions and brand-new approvals.

The company is currently awaiting word from the U.S. Food and Drug Administration concerning its application for odronextamab, a potential new cancer therapy. Further, Dupixent could also earn new indications. And that's just the beginning. Regeneron's pipeline features a few dozen programs. Regeneron's business looks solid, so even as its shares recently soared, investors should strongly consider investing in the stock now before it takes off even higher.

2. Roku

Roku's stock struggled for much of last year for one simple reason: The economy wasn't doing well. As a result, companies decreased their advertising budget -- Roku's most crucial source of revenue. However, management reminded investors that "The significant and long-term opportunity in TV streaming is not changed by the current economic cycle." Roku is proving just how true that statement is this year.

The company's third-quarter results showed solid continued progress. It recorded revenue of $912 million, a 20% year-over-year increase. Roku's active accounts of 75.8 million jumped by 16% compared to the year-ago period. Streaming hours came in at 26.7 billion, 22% higher than the prior-year quarter. It wasn't a flawless earnings report for Roku. Its average revenue per user declined by 7% year over year to $41.03, while its gross margin came in at 40.4% compared to 46.9% in the year-ago period.

Still, Roku's revenue and engagement are moving in the right direction, allowing the company to take advantage of the aforementioned long-term opportunity in TV streaming.

Roku's number of active accounts is just a fraction of Netflix's 247.15 million paying subscribers. However, Roku doesn't directly compete with Netflix or any other streaming channel. Since the company provides a platform that carries most of the prominent streaming services, Roku will profit as streaming continues to steal viewing time away from cable -- which it has been doing for a while.

But there is still a long way to go; streaming accounted for just 37.5% of TV time in September in the U.S., one of the most advanced markets. Further, Roku arguably benefits from a network effect, with growing engagement on the platform making it more valuable to advertisers. Even after its recent jump, Roku's forward price-to-sales (P/S) ratio looks reasonable at about 3.4.

ROKU PS Ratio (Forward) Chart

ROKU PS Ratio (Forward) data by YCharts.

While the undervalued range is generally considered below 2, Roku's P/S multiple is still on the low end of what it has been for the past couple of years. In my view, given Roku's position in the streaming industry and its excellent prospects, the company is worth a premium. That's why now is still a great time to purchase Roku's shares.