CHICAGO (CBS) — The American Cancer Society wants you! It’s looking for 300,000 volunteers between the ages of 30 and 65, and who are cancer-free, to enroll in a 20-year study that seeks to answer the question, “what causes cancer?”

CBS 2’s Kris Gutierrez reports the organization needs 8,000 volunteers in Chicago, and is signing people up for its Cancer Prevention Study – 3 (CPS-3) at its Michigan Avenue office from 8 a.m. to 1:30 p.m. today. First, you must sign up for an appointment, and fill out a medical survey online by clicking here. Other sign-up events will be held throughout the state through late September.

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Dr. LaMar Hasbrouck, director of the Illinois Department of Public Health was urging Illinois residents to take part in the study.

“If you’re not personally touched by cancer yet, you will be,” he said. “Every major link with cancer that we’ve discovered – be it the link between tobacco and cancer, or the link between obesity and cancer – we’ve learned from studies just like this.”

Alan Johnson lost his grandfather to colon cancer five years ago.

“When he went downhill, he went downhill rapidly,” Johnson said. “I remember him passing away, and it was really hard on our family.”

Hasbrouck said it has been estimated that half of men and a third of women will be diagnosed with cancer in their lifetime.

“This year alone, we’re estimating 1.6 million new cases of cancer nationally,” he said.

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To take part in the study, you must be between 30 and 65 years old and never diagnosed with cancer.

Doctors hope CPS-3 will help find new ways to spot trends, and prevent cancer, by monitoring people’s activity over a 20- to 30- year period.

Those interested in taking part will have their blood drawn, their waists measured, and will fill out surveys. Then, there will be regular follow-ups over the length of the study.

“You take a large group of people, and their information, you compile it together, and you look for trends,” American Cancer Society research director Elizabeth Jablonski said. “You have to have this kind of data, in real time, in real life, to look at what it means in the population.”

The hope is to find ways to prevent cancer, so people like Alan Johnson can create even more memories with their loved-ones.

“He imparted so much wisdom on me, and really made me the man I am today, so if I could do anything to make sure that no one else goes through the pain that he went through physically, or the emotional pain that my family went through, I’d definitely sign up for a study like this.”

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For a list of all enrollment events in Illinois, click here.