When you buy a stock there is always a possibility that it could drop 100%. But when you pick a company that is really flourishing, you can make more than 100%. Long term Prothena Corporation plc (NASDAQ:PRTA) shareholders would be well aware of this, since the stock is up 144% in five years. It's also up 18% in about a month.

Since the stock has added US$189m to its market cap in the past week alone, let's see if underlying performance has been driving long-term returns.

Prothena wasn't profitable in the last twelve months, it is unlikely we'll see a strong correlation between its share price and its earnings per share (EPS). Arguably revenue is our next best option. Shareholders of unprofitable companies usually desire strong revenue growth. That's because it's hard to be confident a company will be sustainable if revenue growth is negligible, and it never makes a profit.

In the last 5 years Prothena saw its revenue grow at 40% per year. Even measured against other revenue-focussed companies, that's a good result. So it's not entirely surprising that the share price reflected this performance by increasing at a rate of 20% per year, in that time. So it seems likely that buyers have paid attention to the strong revenue growth. To our minds that makes Prothena worth investigating - it may have its best days ahead.

You can see how earnings and revenue have changed over time in the image below (click on the chart to see the exact values).

Take a more thorough look at Prothena's financial health with this free report on its balance sheet.

A Different Perspective

While the broader market gained around 25% in the last year, Prothena shareholders lost 65%. However, keep in mind that even the best stocks will sometimes underperform the market over a twelve month period. On the bright side, long term shareholders have made money, with a gain of 20% per year over half a decade. It could be that the recent sell-off is an opportunity, so it may be worth checking the fundamental data for signs of a long term growth trend. It's always interesting to track share price performance over the longer term. But to understand Prothena better, we need to consider many other factors. Case in point: We've spotted 1 warning sign for Prothena you should be aware of.

We will like Prothena better if we see some big insider buys. While we wait, check out this free list of undervalued stocks (mostly small caps) with considerable, recent, insider buying.

Please note, the market returns quoted in this article reflect the market weighted average returns of stocks that currently trade on American exchanges.

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This article by Simply Wall St is general in nature. We provide commentary based on historical data and analyst forecasts only using an unbiased methodology and our articles are not intended to be financial advice. It does not constitute a recommendation to buy or sell any stock, and does not take account of your objectives, or your financial situation. We aim to bring you long-term focused analysis driven by fundamental data. Note that our analysis may not factor in the latest price-sensitive company announcements or qualitative material. Simply Wall St has no position in any stocks mentioned.

Have feedback on this article? Concerned about the content? Get in touch with us directly. Alternatively, email editorial-team@simplywallst.com