CHICAGO – Chicago Mayor Rahm Emanuel’s biggest threat, Chicago Teachers Union president Karen Lewis, will not challenge him, numerous media outlets are reporting.

“Karen Lewis has decided not to pursue a mayoral bid,” said Jhatayn Travis, coordinator of the Karen Lewis Exploratory Committee said, according to ABC 7.

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“Yet she charges us to continue fighting for strong neighborhood schools, safe communities, and good jobs for everyone.

“Our work is not about one leader, one race, or one election. Our work is about building progressive power to restore participatory democracy to Chicago. The groundswell of grassroots support is a testament to the strength of our movement and to the depth of dissatisfaction that hardworking Chicagoans have with the top-down, out-of-touch leadership in City Hall,” Travis said.

Lewis’ decision not to run leaves Alderman Bob Fioretti as the main candidate challenging Rahm Emanuel, CBS Chicago notes.

Fioretti issued a statement saying in part, “For Chicago’s sake, I hope this is not the last we see of Karen Lewis. I have the pleasure of calling her a friend, and I join many across this city in praying for her health today. I can understand the battle with illness, and how it can change the best thought out plans. But I also know that Karen is resilient and strong and will be back advocating for educators…students…and Chicagoans in no time.”

Lewis’ decision comes on the heels of news that she was admitted to the hospital citing “discomfort” and had emergency surgery.

“Karen Lewis has a serious illness,” CTU vice president Jesse Sharkey said last week. “She underwent surgery yesterday and that was successful. She is recovering well. … She’s both alert and comfortable.”

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Lewis has reportedly lost more than 100 pounds after she underwent bariatric surgery in Mexico in March.

UPDATE: CBS is reporting Lewis has a “cancerous brain tumor.”