The S&P/ASX 300 Index (ASX: XKO) is up a respectable 7.7% in 2024, but this ASX 300 stock has left those gains far behind.

The high-flying stock in question is biotech company Mesoblast Ltd (ASX: MSB).

On 3 January, the Mesoblast share price closed the day down 4.9% at 29 cents.

That means you could have snapped up 20,689 Mesoblast shares with a $6,000 investment.

In late morning trade today, those same shares were swapping hands for $1.09 apiece, up 275.9%.

If you had decided to sell those shares then, you could have turned that $6,000 investment in this ASX 300 stock January into $22,551.01 today.

Boom!

Here's what's been sending the stock flying higher.

FDA helps send ASX 300 stock soaring

Most of the meteoric gains in the Mesoblast share price this year came in March and April.

In late March, the ASX 300 stock reported on the progress of its remestemcel-L treatment with receiving United States Food and Drug Administration (FDA) approval.

Mesoblast's remestemcel-L is intended to treat inflammatory diseases, including steroid-refractory acute graft versus host disease and biologic-resistant inflammatory bowel disease.

On 26 March, Mesoblast announced the FDA had determined that the results of the additional clinical data from its phase 3 study sufficed to support the resubmission of Mesoblast's proposed Biologics License Application (BLA) for remestemcel-L.

Shares in the ASX 300 stock closed up 45.5% on the day of the FDA announcement, with investors clearly excited about the drug's potential in the world's top economy.

And as word spread, Mesoblast shares kept on charging higher in March, leaping 71.2% in a single day on 2 April despite no fresh news coming out from the company.

What's been happening lately?

Mesoblast shares traded at 52-week plus highs on 23 July, closing the day at $1.31.

While the ASX 300 stock has retraced from that level, shares regained a positive trajectory over the past month, up 15% since 27 August.

Investors initially reacted somewhat negatively to Mesoblast's FY 2024 results, reported on 29 August, with shares closing down 0.5% on the day.

However, the next day the market seemed to have second thoughts about that, with the Mesoblast share price blasting 8.4% higher on 30 August.

Key metrics from the company's full-year results included a 17% year-on-year decline in revenue to US$5.9 million. This was primarily due to lower royalties on Temcell HS sales in Japan.

Despite sizeable cost reductions, Mesoblast reported a net loss after tax of $88.1 million, up from an $81.8 million net loss in FY 2023.

But investors clearly still see this as an ASX 300 growth stock, priced with potential future commercial successes in mind.

Indeed, as Mesoblast CEO Silviu Itescu said on the day of the results announcement, "We are in active discussions with the agency [FDA] and anticipate a decision prior to or on the … goal date of January 7, 2025."

Itescu added:

Concurrently we are implementing a go-to-market plan to bring RYONCIL [remestemcel-L] to the many children suffering with this devastating disease, picking up the substantial amount of work completed last year.