Were the biggest biotechs in the world today always so big? Of course not. They all started out as much smaller companies. Along the way, each of today's big biotechs had a successful product that helped them launch yet another successful product. They made a few acquisitions to drive even higher growth. Over a period of time, the once-small companies grew to be very large.

Three not-so-big biotechs that appear to be on this same path right now are Exelixis (NASDAQ:EXEL), Incyte (NASDAQ:INCY), and Vertex Pharmaceuticals (NASDAQ:VRTX). Here's why these could be three monster biotech stocks in the making.

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Exelixis

Exelixis currently claims a market cap of around $8 billion. The biotech has three products on the market: Cabometyx, Cometriq, and Cotellic. Technically, though, Exelixis only has two approved drugs, because cabozantinib is marketed under both the Cabometyx and Cometriq brand names.

I suspect Exelixis could follow in the footsteps of much larger biotechs. The company achieved a huge milestone in the first quarter of 2017 by posting a profit. It was profitable again in the second quarter. In addition, Exelixis paid off all of its debt this year. This puts the biotech in excellent financial shape to take the next step of beefing up its pipeline.

Michael Morrissey, Exelixis' CEO, recently stated that the company plans to add oncology assets either through partnering with another biotech or making an acquisition. That's smart. There's a good chance that Cabometyx will win regulatory approval as a first-line treatment for kidney cancer. That would increase Exelixis' revenue and cash flow significantly, allowing the company to reinvest to fuel more growth. Repeat this process a few times, and Exelixis' market cap could multiply.

Incyte

Incyte's market cap of $24 billion is already several times larger than Exelixis'. The company became profitable in 2015 thanks to the success of its first approved drug, JAK inhibitor Jakafi. Sales for the drug continue to grow and could reach $2 billion annually.

It didn't take too long for Incyte to use its new-found wealth to add another drug to its lineup. In 2016, the biotech bought ARIAD Pharmaceuticals' (NASDAQ:ARIA) European operations and picked up an exclusive license for ARIAD's leukemia drug Iclusig. Incyte has also invested heavily in its internal research and development efforts, with more than dozen clinical programs.

The next big blockbuster for Incyte could be epacadostat. Market research firm EvaluatePharma ranks epacadostat as the second most-promising cancer drug in late-stage development and expects sales of $1.7 billion by 2022 if it's approved. That could just be the start of a string of pipeline successes. Incyte appears to be well on its way to replicating the stories of much larger biotechs.

Vertex Pharmaceuticals

Vertex Pharmaceuticals is the closest of these three biotechs to becoming truly huge. The company's market cap stands at $38 billion. Vertex reported its first profit in the fourth quarter of 2016 on the back of strong sales growth of its two cystic fibrosis drugs, Kalydeco and Orkambi (which is a combination of Kalydeco and another of Vertex's drugs, lumacaftor). 

The biotech has already used its improving financial position to pave the way for future success. Vertex completed an acquisition of Concert Pharmaceuticals' (NASDAQ:CNCE) CTP-656 cystic fibrosis drug in July. The company is also funding advancement of its pipeline, which includes several combination therapies for cystic fibrosis as well as candidates targeting treatment of acute spinal cord injury and acute pain.

Over the long term, Vertex appears to have a tremendous opportunity for growth in the cystic fibrosis market and potentially in other genetic diseases. Even over the short term, the stock should perform well with continued success for Kalydeco and Orkambi and the likely approval of its combination of tezacaftor and Kalydeco. Vertex could very well become a giant in the genetic disease market in the coming years. 

What could get in the way

A serious clinical setback could definitely prevent any of these three biotechs from reaching the next level. However, I think there's an even bigger threat.

All three of these biotechs have frequently been mentioned as potential buyout targets. That's especially true of Incyte. If efforts to reform corporate taxes in the U.S. are successful, it wouldn't be surprising if one or more of these up-and-coming biotechs are acquired by a larger biopharmaceutical company looking to spur more growth. The greatest risk that Exelixis, Incyte, and Vertex face face in becoming a monster biotech is getting eaten by a biotech that's already a monster.

Keith Speights has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Exelixis. The Motley Fool recommends Vertex Pharmaceuticals. The Motley Fool has a disclosure policy.