Source: Gilead Sciences

Gilead Sciences (NASDAQ:GILD) has won approval for its promising drug Zydelig in three important cancer indications. As a combination treatment alongside Roche's  top selling Rituxan, the FDA green-light puts Zydelig head-to-head against Pharmacyclics' (NASDAQ:PCYC) Imbruvica in relapsing chronic lymphocytic leukemia, or CLL.

While the approval also gives Gilead an opportunity in relapsing follicular lymphoma, and small lymphocytic lymphoma as a stand-alone therapy, investors are right to wonder just how big and crowded the market is already.

In the following slideshow, you'll learn more about each cancer and what the market opportunity may be for Zydelig.

Todd Campbell owns shares of Gilead Sciences. Todd owns E.B. Capital Markets, LLC. E.B. Capital's clients may or may not have positions in the companies mentioned. Todd owns Gundalow Advisors, LLC. Gundalow's clients do not have positions in the companies mentioned. The Motley Fool recommends Gilead Sciences. The Motley Fool owns shares of Gilead Sciences. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.