SAN FRANCISCO (AP) — University of California President Janet Napolitano, a former U.S. Homeland Security secretary, has been undergoing cancer treatment for five months and has been hospitalized after suffering complications, the school system said Tuesday.

The UC Office of the President said Napolitano, 59, was diagnosed last August but did not say what type of cancer she has or respond to inquiries seeking further details. Her condition had not previously been made public and emerged after a side effect from her treatment sent her to the hospital Monday.

Her office said Napolitano has performed her duties at full capacity and is expected to be discharged in the next day or so. The president of the 10-campus system has kept the chairwoman of the UC Board of Regents informed throughout her treatment, which is nearly complete, the university said.

The rest of the Board of Regents learned of Napolitano's cancer diagnosis in a phone call Tuesday morning, which was followed by an email sent by board Chairwoman Monica Lozano.

"As you no doubt have observed, Janet has been able to consistently perform her wide range of duties and extensive travel at full capacity," Lozano wrote in an email. "Yesterday, however, she experienced side effects from her treatment that required her to be briefly hospitalized."

A spokesman for Gov. Jerry Brown, Evan Westrup, confirmed that his office was contacted "ahead of time" about her illness, but he did not respond to a request for more specifics about when the governor was notified.

Napolitano, who previously was treated successfully for breast cancer, was a two-term Democratic governor of Arizona before joining President Barack Obama's Cabinet.

She served as secretary of the Department of Homeland Security from 2009 to 2013, as governor of Arizona from 2003 to 2009, as Arizona's attorney general from 1998 to 2003, and as U.S. attorney for Arizona from 1993 to 1997.

Napolitano now oversees the 10 UC campuses, five medical centers, three affiliated national laboratories, and a statewide agriculture and natural resources program. She is among the highest-paid public employees in the state, receiving an annual $570,000 salary and benefits totaling nearly $150,000 a year.

As president of the system since 2013, Napolitano has fought for additional funding for higher education, and she recently announced a policy saying UC employees will not assist government agencies trying to enforce federal immigration laws. Napolitano has repeatedly sought to ensure undocumented students they can feel safe on UC campuses since the election of Donald Trump, who made illegal immigration a key point of his campaign.

In the past year, she has faced ethics scandals involving the chancellors at two of the largest schools in the system, UC Berkeley and UC Davis, both of whom eventually resigned.

In November 2004, Napolitano had surgery to remove her right ovary and an ovarian cyst, which was benign. She resumed a normal work schedule three days later.

Napolitano had her right breast removed in 2000 after being diagnosed with cancer.

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Associated Press writers Sophia Bollag and Juliet Williams in Sacramento contributed to this report.