Every year thousands of people undergo tests to screen for cancer in the belief that an early diagnosis will help save their lives. But surprisingly, some research suggests that the reasons to screen for -- and treat -- cancer may not be so cut and dry. The Today Show's Matt Lauer has more. For most women over 40, it's a routine part of health care. The American Cancer Society recommends a mammography every year to test for breast cancer. But at 56 years old, Jeanne Lenzer doesn't want one. "My doctor was quite upset with me when I told her I was declining a mammography, and she actually suggested to me that she couldn't have me as a patient if I wasn't going to help myself." She's spent years scouring medical reports as an investigative reporter and has come to the conclusion that early detection won't help her live any longer. "Everybody has to make their own choice // but for me as a healthy woman without having a family history, I just don't feel it's proven." The thinking goes back to a 2005 study in the journal of the national cancer institute which essentially says that all breast cancers detected from a mammogram aren't equal... Some could be life threatening, while others may pose no risk at all. Either way, both types are often treated aggressively. "I figured for me personally, it just wasn't right for me." That fear of unnecessary treatment isn't limited to mammogram patients. Increasingly, questions are being raised about the benefits of other forms of cancer detection, such as colonoscopy for colon cancer. And just this week a study in the journal of the national cancer institute found that the common p-s-a prostate test may lead to over diagnosis. Still... Some doctors would rather be safe than sorry. "Screening is imperfect. We need to continue screening, we have to recognize the limitations of screening." A continuing debate that's raising even more questions for patients concerned about their long-term health.