For more than a decade, growth stocks have been unstoppable. Abundant access to cheap capital and historically low lending rates have allowed fast-growing businesses to hire, acquire, and put their innovative prowess to work.

But for some companies, their growth is just getting started. For the following four under-the-radar small-cap growth stocks, Wall Street expects sales to increase by 707% to as much as 9,406% over the next four years.

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Bionano Genomics: Implied sales growth of 1,182% by 2024

First up is small-cap genome analysis company Bionano Genomics (NASDAQ:BNGO). Wall Street expects Bionano's sales will grow from a reported $8.5 million in 2020 to approximately $109 million by 2024. That's a cool 1,182% projected increase by 2024, for those of you keeping score at home.

The excitement surrounding Bionano has to do with its optical genome mapping (OGM) system, Saphyr. Back in December, Bionano's share price skyrocketed after the company published a study where Saphyr appeared to outperform Pacific Biosciences' OGM technology. Specifically, Saphyr was shown to be more sensitive at identifying large structural genome variations than Pacific Biosciences' OGM technology. 

Just a few weeks later, Bionano announced that it had identified three risk genes for autism spectrum disorder using Saphyr. The point being that Bionano is showcasing the capabilities of its OGM technology in the hope that drug developers will deploy it to tackle gene-specific and hard-to-treat diseases.

The big question mark at this point is whether Bionano Genomics will receive reimbursement in the U.S. for Saphyr. With the product still likely years away from a Food and Drug Administration review, it's unclear where orders and recurring revenue could come from. Don't get me wrong, the product is exciting. But with losses expected to continue for the foreseeable future, shareholders will have to exercise a lot of patience.

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Columbia Care: Implied sales growth of 707% by 2024

Marijuana stocks are expected to deliver exceptional growth across the board over the next four years. This includes the little-followed U.S. multi-state operator Columbia Care (OTC:CCHWF), which is forecast to see full-year sales catapult by 707%, from $179.5 million in 2020 to an estimated $1.449 billion by 2024.

While some investors might be leery about putting their money to work in pot stocks with the federal government stalling on cannabis legalization, this isn't the issue it might seem. We've witnessed 36 states legalize medical marijuana, half of which also have laws on their books to allow adult-use consumption and/or retail sale. There's more than enough organic growth potential at the individual state level for companies like Columbia Care to thrive.

What makes Columbia Care such an intriguing company is its reliance on acquisitions. This includes the recently completed $240 million deal to buy Green Leaf Medical, which bolsters the company's mid-Atlantic presence.  Although growth by acquisition can drive up near-term costs, it should allow Columbia Care to begin reaping the rewards of its deals beginning in 2022.

Management has also focused a lot of the company's attention on limited-license markets. States that purposely rein in competition by limiting the number of dispensary licenses they issue should help Columbia Care build up its brands and establish a loyal following.

If the company can turn the corner to recurring profitability in 2022, it could be quite the steal.

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Blink Charging: Implied sales growth of 1,489% by 2024

Another small-cap stock with big-time revenue upside is electric vehicle charging equipment and services provider Blink Charging (NASDAQ:BLNK). Blink recorded $6.23 million in full-year sales in 2020, but is expected to generate $99 million in sales by 2024. That's nearly a 1,500% increase in four years.

The clear and obvious catalyst for Blink is the electrification of automobiles in the U.S. (and globally). In an effort to fight climate change, we're liable to witness a multi-decade vehicle replacement cycle for consumers and businesses. This replacement cycle will be just as much a win for ancillary infrastructure players like Blink Charging as it'll be for EV manufacturers. Providing charging equipment and owning charging stations could allow Blink to play a key role in the green evolution of the auto industry.

Although the upside catalyst here is plain as day, and the company has raised enough capital via stock sales to make a handful of acquisitions, the big thing lacking here is differentiation. A quick look at Blink Charging's income statements suggest it isn't spending any of its capital on research and development. Without leaning on innovation in a trend that's entirely dependent on standing out, I have to wonder if Blink Charging won't be left in the dust by other EV charging equipment providers.

Additionally, the company looks to be many years away from profitability. Even though Wall Street has been lenient in valuing high-growth stocks, a multiple of nearly 13 times sales for 2024 with ongoing losses is an eyebrow-raiser, and not in a good way.

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Vaxart: Implied sales growth of 9,406% by 2024

For the crème de la crème of growth among small-cap stocks, at least on this list, we turn to clinical-stage biotech stock Vaxart (NASDAQ:VXRT). After delivering $4.05 million in revenue last year, Wall Street's consensus is for the company to generate $385 million in full-year sales by 2024. That's more than a 9,400% sales increase in four years.

Vaxart's future success rests with its VAAST platform. VAAST stands for Vector-Adjuvant-Antigen Standardized Technology. Without getting too technical, there are two important things to know about VAAST. First, it's targeted at developing proprietary oral vaccines, as opposed to those less-than-pleasant jabs in the arm. Second, VAAST is designed to activate systemic and mucosal immunity in the nose, lungs, intestines, and mouth. Whereas traditional vaccines activate systemic immunity, an oral vaccine via the VAAST platform could provide added protection via systemic and mucosal activation.

Although Vaxart has a handful of promising early-stage clinical and pre-clinical drug candidates, it's the company's work in developing an oral coronavirus vaccine (VXA-CoV2-1) that put it on the map. The idea is that it would be considerably easier to distribute and administer an oral vaccine.

However, it's important to note that Vaxart is still in the very early clinical stages of developing an oral COVID vaccine. What's more, data released from a phase 1 trial of VXA-CoV2-1 in early May showed a notable immune response, but it didn't lead to high levels of neutralizing antibodies in study participants. This could make it a less-attractive option in preventing COVID infection.

Suffice it to say, oral vaccines sound great on paper, but they're a long way from becoming a reality.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.