Screening tests can find cancer early -- so why do some experts say they can do more harm than good? Read this before your next mammogram, PSA test, or colonoscopy.Suzanne Bull always half expected that she'd get cancer. After all, she lived in Marin County, California, where breast cancer rates are among the highest in the country. Still, she was determined to do whatever she could to protect herself. She ate right and exercised, and every year, she went into San Francisco to get a mammogram. #