Biotech stocks have taken a punishing nose-dive over the past month as investors step aside following significant gains. However, the current share slide is likely more a result of emotion than any long-term changes at drug developer heavyweights Celgene (NASDAQ:CELG), AbbVie (NYSE:ABBV), and Gilead (NASDAQ:GILD).

All three have blockbuster therapies that are likely to drive sales higher, rather than lower, this year. Since all three are set to report earnings later this month, let's look at what investors will be focusing on.

CELG Chart

CELG data by YCharts

One proven and one potential blockbuster
Celgene has long benefited from Revlimid's market share leadership as a myeloma treatment. The company sold more than $4 billion worth of Revlimid last year alone. But it's not just Revlimid that investors will be watching when Celgene reports earnings on April 24.

Investors will also be zooming in on Abraxane, Celgene's promising cancer therapy. Abraxane won FDA approval for pancreatic cancer last fall, and sales have jumped sharply since coming to market as a treatment for non-small-cell lung cancer in 2012. Based on its fourth-quarter sales, Abraxane could be destined to hit the $1 billion blockbuster plateau this year.

Additionally, investors will want to see whether Celgene offers any clues on prescribing trends for its newly launched Otezla. Otezla won the FDA go-ahead as a treatment for psoriatic arthritis in March, so Q1 earnings may provide insight into inventory builds at drug wholesalers.

Heading into Celgene's report, industry analysts expect the company to report earnings per share of $1.65, up from $1.37 last year. If the company can beat those estimates, shares could head higher as analysts boost their full-year forecast, which currently stands at $7.28.

Eyes on the future
Investors holding on to AbbVie's shares after it was split from Abbott Labs early in 2013 have been handsomely rewarded. However, the ability for AbbVie to keep climbing is going to rely on Humira's ability to fend off competitors.

Humira, the nation's best-selling drug with $10.7 billion in sales last year, accounts for roughly half of AbbVie's sales, and revenue growth for the drug last year helped AbbVie's earnings per share grow sequentially during every quarter of 2013.

Currently, analysts predict AbbVie will report earnings of $0.68 per share on April 25. If so, investors may be disappointed, since the company similarly earned $0.68 last year.

However, Humira won't be the only thing investors will be watching in AbbVie's report. AbbVie has been ushering a promising three-drug combination therapy for hepatitis C through trials that some think could become the second best selling drug for that indication behind Gilead's recently launched Sovaldi. AbbVie previously said it would file for FDA approval of the regimen by midyear, and it's likely that management will provide an update on that timeline during the conference call.

Realizing blockbuster potential
Even if AbbVie does submit its hepatitis C drug for approval soon, it will have a lot of ground to make up on Gilead's Sovaldi. The FDA approved Sovaldi as a hepatitis C treatment in December, and despite only being available for a few weeks, Gilead still sold $140 million worth of the drug in the fourth quarter.

That has investors eager to see whether Gilead's Sovaldi has already achieved a blockbuster sales run rate in the first quarter. If so, Sovaldi could become one of the fastest drugs ever to reach the $1 billion annual sales mark this year.

However, Sovaldi is just one of Gilead's successes. Sales of the company's HIV drugs are also growing rapidly. Revenue from Gilead's HIV drugs totaled more than $9 billion in 2013, up 15% from 2012, and that momentum is likely to have carried though into the first quarter.

Currently, analysts expect Gilead's earnings per share to total $0.85 for the first quarter. However, those expectations are considerably higher than the $0.65 analysts were projecting just 90 days ago. That means the hurdle has been set high. If Gilead delivers the $0.85, it will mark a 77% jump from last year. Even if Gilead beats that forecast, analysts may not bump up their full-year forecast. After all, they already expect Gilead to earn $3.99 per share in 2014, up from $3.30 estimates three months ago.

Fool-worthy final thoughts
Few have the reputation for success of these three companies, and investors are likely eager to see if each can meet or beat first-quarter predictions. If so, investors having sold shares in Celgene, AbbVie, and Gilead may be forced to reconsider. After all, all three have not only billion-dollar franchises kicking off substantial cash flow, but pipelines that could help drive sales higher in the future, too.