If I told you that a $5,000 investment in an ASX 300 healthcare stock just one year ago would be worth $30,000 today, you might be a little sceptical. 

After all, that kind of return (500%), especially among the larger companies on the ASX, is an exceptionally rare feat. It certainly beats the pants off most of the popular stocks on the ASX 300, including BHP Group Ltd (ASX: BHP) and Commonwealth Bank of Australia (ASX: CBA).

It's even far greater than the returns of popular growth winners like WiseTech Global Ltd (ASX: WTC), Pro Medicus Limited (ASX: PME) and Xero Ltd (ASX: XRO).

So, what is this highly lucrative ASX 300 stock? Well, it's none other than biotech company Mesoblast Ltd (ASX: MSB).

Yep, one year ago, you could have bought this ASX 300 stock for just 27 cents a pop. Today, those same shares are going for $1.63 each.

That means if one had put $5,000 into Mesoblast shares in December of 2023, they would have been able to amass 18,518 shares (not accounting for brokerage costs). Today, those 18,518 shares would have a value of $30,184.34. Not a bad return for just one year of waiting.

So, how has this ASX 300 healthcare stock delivered such an eye-watering gain in so little time?

How has this ASX 300 healthcare stock rocketed 500% in a year?

Well, Mesoblast regularly experiences the same double-edged sword that most other biotech companies do. Investors tend to flood in when the company is expected to successfully bring a product to market. But equally, investors can bail out en masse if the company experiences setbacks in these endeavours.

A year ago, Mesoblast was in the middle of one of those latter cycles. Its attempts to bring an anti-inflammation drug to market had been met with numerous setbacks, including rejections from government agencies like the US Food and Drug Administration (FDA).

However, all of that changed in late March of this year. As we covered at the time, Mesoblast revealed that the FDA had finally given the company approval to submit a Biologics License Application (BLA) for its 'Ryoncil' remestemcel-L treatment.

The company's shares promptly rocketed close to 200% over the following week or so and have continued to trend upward ever since.

It's clear that investors anticipate that this ASX 300 healthcare stock will continue to find success with Ryoncil and have adjusted the Mesoblast share price accordingly. The company itself shares that confidence, with Mesoblast already initiating a convertible note subscription with its biggest investors that will give it access to additional capital if the FDA gives Ryoncil approval.

Foolish takeaway

Before you turn green with envy though, it's worth noting that this ASX 300 healthcare stock has only been a lucrative investment for a handful of buyers. If you owned this stock for more than a few years, chances are you might still be nursing a loss.

Despite the astonishing gains that Mesoblast shares have made over the past 12 months, this ASX 300 healthcare stock is down by 15% over the past five years. In fact, any investor who bought this company back in August 2020 would still be sitting on a loss of more than 68% today.

Check that out for yourself below before you go: