The company said it expects an operating profit of 263 billion yen ($2.4 billion) for the year ending March 31, higher than analysts' average expectation of 256 billion yen, according to IBES data from Refinitiv. Astellas reported an annual operating profit of 244 billion yen last year.
Shares in the company closed 2.4% higher in Tokyo compared with a 1% rise in the broader market.
Sales of Xtandi rose 18% to 298 billion yen in the third quarter ended Dec. 31.
However, core operating profit for the quarter was 3.3% lower, hurt partly by a 2.5% drop in revenue from Prograf, used to prevent rejection of organ transplants.
The company also said it will book a one-off charge of about $100 million in the fourth quarter related to its purchase of U.S.-based biotech Audentes Therapeutics Inc.
Astellas, the country's second-biggest drugmaker by sales, has ramped up overseas acquisitions to broaden its drug pipeline.
The company said in December it would pay up to $665 billion for Xyphos Biosciences Inc to expand its immuno-oncology business. Earlier that month, Astellas said it would purchase Audentes in a deal worth $2.65 billion to expand into genetic medicines.
Both Xyphos and Audentes are based in San Francisco, a hub for biotech companies that are fetching huge premiums for global pharma firms eager to bolster their drug pipelines.
Among other major Japanese pharma companies reporting earnings, Daiichi Sankyo Co, Japan's fourth-largest drug company by sales, raised its full-year operating profit forecast, citing lower taxes. It expects to earn 135 billion yen in the year ending March 31 versus 125 billion predicted in October.
Eisai Co, the partner of Biogen Inc on Alzheimer's disease drug candidate aducanumab, maintained its full-year operating profit forecast at 110 billion yen, a 16% increase from last year, driven by sales of its cancer drug Lenvima.
Daiichi Sankyo shares rose 1.6% while Eisai gained 2.2%.
By Rocky Swift