SOUTH BEND -- When it comes to cancer screenings, ignorance is not bliss.

Knowledge and discussions with one's doctor can help a person decide which tests are right and when, five local physicians said Wednesday night during a panel discussion at Indiana University School of Medicine-South Bend about the pros and cons of cancer screenings.

Cancer screenings are useful when the test can detect a tumor at an early stage and treatments exist for that cancer that improve survival rates, said Dr. Rudolph Navari, an oncologist and director of the IU School of Medicine-South Bend.

"For all screenings, sit down with your doctor and have a candid conversation about what is right for you," Navari said.

Among American men, the top three most diagnosed cancers are prostate, followed by lung and colorectal cancers. Among American women, the top cancer diagnosed is breast cancer, followed by lung and colorectal.

Screening for colorectal cancer generally involves colonoscopy at age 50 and each 10 years after that, said Dr. Patrick O'Dea, a gastroenterologist. However, only about half of adults 50 and older have the testing consistent with the guidelines, he said.

Colonoscopy can detect polyps, benign growths that are easily removed before they develop into cancer. "Removing the polyps reduces the cancer risk by 75 to 90 percent," O'Dea said.

If a close relative -- a parent or sibling -- was diagnosed with colon cancer before age 60, one is at increased risk and generally should start screening earlier and more often, he said.

Although recommendations regarding breast cancer screenings have changed over the years, Dr. Samir Patel, a radiologist, advocates the standard of annual mammograms for most women starting at age 40.

Breast cancer remains the No. 2 most common cause of cancer deaths among women. Studies show that for women who undergo annual mammograms beginning at age 40, their mortality rate is reduced 30 to 45 percent, Patel said.

"The key is early detection," he said, noting one out of every five cases of breast cancer is diagnosed in women in their 40s.

Although some women worry that the small amount of radiation from mammograms will cause them to develop cancer, a woman actually is more likely to be struck by lightning than to develop breast cancer from screening mammograms, he said.

Similarly, recommendations about Pap smears to test women for cervical cancer have varied over the years, said Dr. Etta Nevel, a gynecologist. Guidelines today are related to individual risk factors, and some women don't need an annual Pap test, she said.

Many young women catch the virus that causes cervical cancer as young adults through sexual contact, but it often clears up on its own by the time a woman is in her 30s, Nevel said. Two vaccines now available prevent most cases of cervical cancer if given before a female is exposed to the virus.

Ovarian cancer remains a tough cancer to screen for, because methods of testing aren't yet very reliable, Nevel said.

Prostate cancer screening is controversial, because although it's the most common cancer in men, it's generally slow growing, said Dr. Can Talug, a urologist. One in every six men will be diagnosed with prostate cancer, but the vast majority will die of some other cause, he said.

The American Urological Association recommends prostate screening starting at age 40. Such screening isn't appropriate for everyone, and each man should talk with his doctor about the risks and benefits, Talug said.

Twenty-five percent of all cancer deaths are from lung cancer, overwhelmingly caused by smoking, Navari said. "It's never too late to quit," he said, noting that smokers who quit before age 30 quickly fall to the same lung cancer risk as non-smokers.

Cases of melanoma, the most dangerous type of skin cancer, are rapidly rising, Navari said. It's now the fourth most diagnosed cancer among men, and sixth among women.

That increase isn't just related to sunbathing, but also to rising use of tanning salons, Navari said. "If I see one of my students with a tan in South Bend in January, I confront them about that," he said.

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Staff writer Margaret Fosmoe: