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' (UNKNOWN:PCYC.DL) 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.