Exelixis (NASDAQ: EXEL) was one of the top biotech stocks of 2016. It’s also one of the best biotech stocks so far this year. However, Exelixis shares have pulled back in recent days, primarily due to Bristol-Myers Squibb‘s (NYSE: BMY) announcement that it was halting a late-stage study of Opdivo and Yervoy in treating first-line renal cell carcinoma (RCC) earlier than expected because of positive results.