The drugmaker Gilead Sciences said on Monday that it would buy Kite Pharma for about $11.9 billion to bolster its aging portfolio with an emerging cancer treatment.

The acquisition, Gilead’s first major deal since 2011, is a departure from the path followed by the broader pharmaceutical industry, where — apart from Johnson & Johnson’s $30 billion takeover of the Swiss biotechnology company Actelion — the pace of acquisitions had largely slowed this year. Many drugmakers that had been busy with takeover activity in recent years have since been at work integrating their purchases.

Under the terms of the agreement, Gilead will pay $180 a share in cash, a 29 percent premium to Kite’s closing price on Friday.

With the deal, Gilead would acquire Kite’s new cancer-fighting method, which harnesses the body’s immune system to attack malignant cells. Kite’s most promising treatment, for non-Hodgkin lymphoma, is expected to receive government approval within the next year.