The price is 39 percent higher than Pharmacyclics’s closing price on Feb. 24, the day before Bloomberg News reported that the company was considering a deal. The purchase would help AbbVie reduce its reliance on Humira, its best-selling rheumatoid arthritis treatment while expanding into cancer therapy, one of the most promising areas of drug development. It would gain control of Imbruvica, an easy-to-use pill that costs about $100,000 a year, avoids certain serious side effects of chemotherapy, and is already approved for four different blood cancer uses.