CHICAGO (CBS) — Chicago Teachers Union president Karen Lewis is undergoing medical procedure on Wednesday, sources said.

Lewis was first diagnosed with an aggressive form of brain cancer in 2014. The nature of today’s procedure was not immediately disclosed, but published reports said it was brain surgery.

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“I spoke with Karen yesterday. who is in great spirits and advised us that she had planned a medical procedure today in the hospital,” said CTU vice president Jesse Sharkey. “We had hoped to wait to make a public statement until we’d had a chance to update our members directly at tonight’s House of Delegates meeting – the last of the school year.”

“As we all know, Karen is a fighter. She is looking forward to the coming rallies, actions and negotiations.”

In October, Lewis suffered a stroke in the same area of the brain where she had a tumor removed in 2014.

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Lewis’ brain cancer diagnosis in 2014 derailed plans to run against Mayor Emanuel in 2015. She ended up backing Cook County Commissioner Jesus “Chuy” Garcia, who forced Emanuel into a runoff, the first ever in a Chicago mayor’s race.

Lewis had never officially declared her candidacy, but she did form an exploratory committee and was collecting signatures.

While she didn’t end up running for mayor, Lewis led contract negotiations with the Chicago Public Schools in 2016. The union agreed to a four-year pact that avoided a second teachers’ strike under the Emanuel administration.

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CPS CEO Dr. Janice Jackson released a statement which said in part “anyone who knows Karen will say she’s a fighter, but I’ve also seen the kinder, gentler side of Karen and am honored to call her a partner and a friend. On behalf of the CPS students, parents, families, and educators, I wish Karen Lewis a full and speedy recovery.”