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For those who invested in Nvidia stock back in the day and held on, the returns have been staggering. It has delivered a 10-year annualised return of 75.3% in sterling terms.
One FTSE 250 investment trust that has benefited is Baillie Gifford US Growth Trust. Between March 2018 and late 2025, its investment in Nvidia went up 3,155%!
Given Baillie Gifford’s track record of unearthing top growth stocks like Nvidia and Tesla, it’s worth keeping an eye on what new shares it has been buying. And one new name in the US Growth Trust’s portfolio caught my eye.
Let’s take a closer look at this under-the-radar company — which recently went public and is already one of the trust’s larger holdings — to see what the fuss is about.
The stock
BillionToOne (NASDAQ:BLLN) is a medical diagnostics company. Its Quantitative Counting Templates platform is the only patented technology that can count DNA molecules with singular precision at a large scale.
Having dug into the firm, I see a few attractive things here. For starters, BillionToOne is operating in two high-growth diagnostics markets: non-invasive prenatal and cancer testing. The firm estimates its total addressable market at roughly $100bn in the US alone.
It’s encouraging to see the firm taking advantage of this opportunity, with Q3 revenue surging 117% year on year to $83.5m. It delivered 165,000 tests, an increase of 52%.
Management is guiding for 2026 revenue of $415m to $430m, which would represent growth of 40% to 45%. Most of its revenue comes from prenatal tests, which screen for conditions like cystic fibrosis and sickle cell using only the mother’s blood, but its cancer tests are growing very strongly.
Another positive is that the company isn’t burning through cash. It expects to report positive full-year operating profit, with strong gross margins of about 70%. So this has the potential to be a very high-margin business.
Finally, the company’s market cap today is just $3.9bn. In this day and age, that’s really not very big. The firm could become much larger if it seizes the commercial opportunity ahead.
After all, Nvidia’s market cap was roughly this size back in 2013.
Our long-term goal is to build a category-defining generational company and become a member of the S&P 500.
BillionToOne
My initial takeaway
Stepping back, I see a few things here that indicate BillionToOne could become a top growth stock. Unlike many early-stage growth firms, it’s already guiding for strong margins and sustained profitability through 2026.
On top of this, there’s solid institutional investor backing and a massive international expansion opportunity. It’s also working on tests that detect cancer early, which could become the most exciting market of all.
However, it’s far too early to call this one a slam-dunk winner, let alone assign it Nvidia-esque potential. There’s a lot of competition in this space from Guardant Health and Natera, and I worry a new diagnostic breakthrough might threaten the firm’s technology at some point.
Meanwhile, the price-to-sales multiple is almost 10, so there’s plenty of growth already baked into the current valuation.
For now, I reckon it’s one to keep an eye on. BillionToOne will report Q4 earnings in early March.
