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University of California President Janet Napolitano has been hospitalized for side effects related to cancer, which was diagnosed in August but made public only on Tuesday.

Napolitano, who ran the Department of Homeland Security before leaving in 2013 to take over the 10-campus UC system, “has consistently performed her wide range of duties at full capacity, without interruption or impact” since beginning treatment for cancer last summer, according to a statement from her office.

UC officials said Napolitano previously had cancer and was successfully treated.

Napolitano, who is nearly done with cancer treatments, “kept the chair of the UC Board of Regents informed,” the statement said.

On Monday, Napolitano experienced side effects that sent her to the hospital, but is doing “extremely well” and is expected to be discharged this week, according to the statement.

Her spokeswoman, Dianne Klein, declined to say what kind of cancer it is, citing the president’s privacy.

Napolitano had a mastectomy in 2000. She went on to become governor of Arizona in 2003, and in 2009 became the first woman to head Homeland Security.

In February, she wrote a “Dear Colleagues” letter inviting UC employees to use their state income tax returns to contribute to the California Breast Cancer Research Fund and the California Cancer Research Fund.

“These programs have a real impact on a disease that touches so many of us,” she wrote.

Regent Eloy Ortiz Oakley, chancellor of the state’s community college system, opened Tuesday’s meeting of the Board of Governors by wishing Napolitano a speedy recovery.

UC Berkeley Chancellor Nicholas Dirks echoed the sentiment and said through a spokeswoman that Napolitano “has shown remarkable strength and resilience, and all of us at UC Berkeley send her our best wishes at this difficult time.”

Nanette Asimov is a San Francisco Chronicle staff writer. Email: nasimov@sfchronicle.com Twitter: @NanetteAsimov