Corcept Therapeutics (CORT 2.18%) is one hot biotech stock no matter how you look at it. Shares have nearly quintupled in value in just three years. So far in 2017, Corcept stock is up around 70%.

Those kinds of returns could make millionaires out of some investors if the momentum continues. But is it too late to buy Corcept stock now? Here are the arguments for both answers to this question.

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Negative Nellies

If you pay attention to what Wall Street thinks, the verdict is split on Corcept Therapeutics. Half of the analysts covering the biotech have a "buy" or "strong buy" rating for the stock. The other half of the analysts have an "underperform" or "sell" rating.

Why would half of these Wall Street analysts have a negative view of the biotech? We can know for sure why at least one of them doesn't view the stock in a favorable light.

In April, a Janney Montgomery Scott analyst reiterated a sell rating for Corcept over concerns that the company is too dependent on Cushing's syndrome drug Korlym and has a weak pipeline. There's no disputing that Corcept relies on Korlym -- it's the biotech's only approved drug, after all.  

What about Corcept's pipeline? It's also true that the company isn't likely to have another approved drug for quite a while. Corcept does have three candidates in its pipeline. Two of them, however, are only in pre-clinical testing. CORT125134 is being evaluated in a couple of phase 2 studies, one for treating Cushing's syndrome and the other in combination with Celgene's (NASDAQ: CELG) Abraxane in treating solid tumors.

Some might simply think that Corcept stock has become overvalued. Shares currently trade at 24 times expected earnings. That's more expensive than many biotechs with multiple blockbuster drugs already on the market.

There's also the threat of competition. Novartis (NVS -0.49%) already has a Cushing's disease drug on the market and is developing a new drug, osilodrostat, that could be more effective. The Swiss drugmaker is evaluating osilodrostat in a phase 3 study for treatment of Cushing's disease and in a phase 2 study for treatment of Cushing's syndrome. 

Stonebridge Biopharma (SBBP) also could have a rival to Korlym on the way. The biotech is evaluating Recorlev in a late-stage study for treating Cushing's syndrome. 

Green signs that say "optimism" and "pessimism."

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Eternal optimists

But why do the other half of Wall Street analysts like Corcept? For one thing, the company has already proven the pessimism to be wrong to some extent.

Corcept posted great numbers in its first-quarter results. They were so good, in fact, that the biotech raised its full-year 2017 revenue guidance. It's important to understand why sales for Korlym were strong. A major factor is that physicians are prescribing the drug more for less severe cases of hypercortisolism.  

In large part because of this trend, the consensus is that Corcept will be able to grow earnings by more than 50% annually over the next five years. That level of growth puts the biotech's stock valuation in an entirely different light. Corcept's PEG ratio is only 0.84. Legendary investor Peter Lynch would be the first to tell you that a stock with a PEG ratio that low is a bargain.

Furthermore, there's reason to be optimistic about Corcept's pipeline. CORT125134 holds the potential to be just as effective at treating Cushing's syndrome as Korlym is but without some of Korlym's negative side effects. That should be important in defending market share from potential rival drugs that could be on the way from Novartis and Stonebridge Biopharma. Results from the phase 2 study are expected by the end of this year. 

Too late?

Is it too late to buy Corcept stock or can investors still jump on board? I'll side with the optimists.

Granted, it's entirely possible that earnings growth estimates for the biotech could prove to be too high. Even with sales for Korlym continuing to increase rapidly, Corcept will spend more on development as it advances its pre-clinical drugs into phase 1 studies.

Still, I like the prospects for both Corcept and Korlym. As for the negative Nellies, I'd just note that the average one-year price target for Corcept stock is $11 per share. Corcept has traded above that level for most of the past two months.