WASHINGTON — Pharmaceutical giant Pfizer Inc. is paying $14 billion to buy Medivation Inc., a San Francisco biotech company that sells a high-priced prostate cancer medication discovered by UCLA.

A year’s worth of the drug, Xtandi, sells for about $129,000, and the medicine has generated about $2.2 billion in net sales worldwide over the last year, the companies said Monday in announcing the deal.

The potential for Xtandi in the growing market for cancer medicines — it’s also being tested for breast cancer treatment — made Medivation a target of larger pharmaceutical companies.

Pfizer Chief Executive Ian Read said “the value of Xtandi and its future growth potential was the principal driver” of the deal.

“With this acquisition, we are expanding and strengthening our footprint in one of the highest-growth therapeutic areas in the biopharmaceutical industry,” he told analysts on a conference call.

New York-based Pfizer agreed to pay $81.50 in cash for each share of Medivation, a 21 percent premium over Friday’s closing price of $67.16.

Medivation stock closed up $13.26, or 20 percent, to $80.42 on Monday. Pfizer shares were down 14 cents, or 0.4 percent, to close at $34.84.