CHICAGO (CBS) — Spin classes this weekend in Chicago and across the country have been helping to raise money for cancer research.

Dave and Jenn Linn came up with the idea of ‘Cycle for Survival’ in 2007 after Jenn was diagnosed with sarcoma, an uncommon group of cancer that arises in the bones and connective tissue.

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“We were really surprised to see how few treatment options there were for these rare cancers,” Dave said. “But when you add them up, they actually make up 50 percent of all cancer cases.”

He added that they decided to help devote more funds to finding a cure for rare forms of cancer.

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Jenn passed away in 2011, before seeing how far the fundraiser has grown.

Chicago is one of six locations hosting spin classes this weekend. Ten other locations are slated for different times in February and March.

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Dave said Cycle for Survival has grown to include 31,000 riders and has raised $125 million for research over the years.