What: Shares of biotech blue chip stock Gilead Sciences (NASDAQ:GILD) catapulted higher by 12% in May, based on data from S&P Capital IQ, after announcing better-than-expected first-quarter earnings results and providing a positive update on its next-generation HIV treatment in Europe.

So what: The big driver for Gilead Sciences, as it's been for some time now, is its hepatitis C duo of Harvoni and Sovaldi. In the first quarter, Harvoni generated sales of a whopping $3.58 billion worldwide, and crushed its only other foe on the market (Viekira Pak) in the U.S. ($3.02 billion in U.S. sales, compared to just $138 million). Sovaldi "chipped in" with an additional $972 million in sales, which is actually down after Harvoni's approval relegated it to the lesser common genotype 2 and 3 HCV. Additionally, HIV pill Stribild generated $356 million in global sales, up from $215 million in the prior-year quarter.

Source: Gilead Sciences.

Overall, Gilead produced $7.59 billion in revenue and a practical doubling of its EPS to $2.94. Comparatively, Wall Street was looking for $6.89 billion in sales and just $2.32 in EPS -- so Gilead crushed it!

The other share price driver came toward the end of the month with Gilead's announcement that the European Medicines Agency (the FDA of Europe) had validated its marketing application for the fixed-dose combination of emtricitabine and tenofovir alafenamide for HIV treatment. In short, it means its application can now come under the review of the EMA. With it appearing to be a superior treatment to Viread, an approval seems to be a better than 50-50 chance in my personal opinion.

Now what: Consider this just another month of business as usual for Gilead Sciences.

Although Gilead will likely face tougher HCV competition in the coming months, for now it remains the convenience leader -- especially in genotype 1 HCV where patients can take Harvoni once-daily without the need for ribavirin or IV interferon. By a similar token, its advancements in HIV and other liver diseases, including hepatitis B and nonalcoholic steatohepatitis (known also as NASH), could put it on track to deliver a number of new blockbusters in the coming years.

Gilead's forward P/E of 10 and double-digit sales growth continue to place its PEG ratio -- a measure of value based on future growth prospects -- around or below one, which would signify that even after its multi-year run higher it's still pretty cheap by most fundamental standards. I'd continue to encourage investors with a modest appetite for risk to take a closer look at Gilead, because you might like what you find.