To most people, the mantra for cancer screening seems pretty clear: "Just do it." But last summer, a government advisory group recommended that men age 75 and older stop getting screened for prostate cancer, after research showed that testing didn't increase their lifespan and likely caused some harm. Then mammograms for women 80 and older were called into question. Colon cancer screening was next: Some experts now say no one over age 85 should get it.

After years of urging us to get regular cancer screenings, how could not knowing you have cancer be a good thing? Tests, especially as you become more experienced (a euphemism for having celebrated more birthdays), involve more trade-offs than negotiating with your kids for the remote in a one-TV household.

The main downside to certain cancer screenings for some groups of people:

They can hurt you. X-rays and mammograms involve radiation, which increase cancer risk. For example, if you get a total-body CT scan and do follow-ups of one suspicious lesion annually for 24 years, that process has a 4 percent chance of causing you to have a cancer. Biopsies may require anesthesia, and the surgery plus drugs are associated with cognitive problems (at least short term, or even marriage proposals to some nurses) for older patients, and infections can occur.

They're often wrong. Cancer tests often have false positives, which suggest a cancer that isn't there. This means you get put through additional tests and procedures that all have risks, not to mention stress to you and your family.

Finding cancer may not do you any good. If you've reached your 80s without developing cancer, the odds that you'll develop a fatal tumor are low. And treating it may not lengthen your life. In the worst case, you could become ill from treating a cancer that would have never caused symptoms.

It could take the focus off what's really important. If you're older, problems such as heart disease and diabetes are much likelier to be fatal than a newly detected cancer. Concentrate on controlling or reversing those. After all, if your brakes are shot, panicking over rust on your fender isn't a wise use of your energy.

It's expensive. At the societal level, testing older people for certain cancers costs a lot and may only benefit a few. Doesn't seem fair to not test if you're one of the few, but the odds are with you.

So what should you do?

Talk with your doctor to create a cancer screening schedule that's tailored for you, not the "average patient." Here's what to keep in mind:

Most guidelines haven't changed. Don't miss the ones your doctor recommends.

Ask this before scheduling any cancer test: How many years can I reasonably expect to live, and during that time, which is more likely to hurt me - this cancer test and treatment risks or an untreated cancer?

Don't rely on your age. We schedule our own health tests based on our functional ages. Dr. Mike, for instance, is 62 by the calendar, but his functional age - determined by his fitness level, blood tests and other variables - is 43. (Determine your own functional age at RealAge.com.)

When we reach 75, we both aim to have functional ages of 55, so we're going to continue to get the screenings recommended for 55-year-old men, in addition to any new ones recommended for 75-year-olds.

Live like you have cancer. What healthy changes would you make if you had cancer? Would you eat more vegetables, take a daily multivitamin or exercise more? Do those things now! You don't need cancer to know that they'll improve your life.

Remember, this is the age of miracle and wonder. We may enjoy some health breakthroughs in the coming decades.

If you're a 75-year old woman in average health, you're projected to die in about 12 years - most likely of heart disease. But what if there's a breakthrough in treating heart disease, and lifespans suddenly increase?

Hey, research is under way on all sorts of life-extenders.

If the new pills that mimic life-extending calorie restriction come through, we could all end up living until age 120.

The You Docs - Mike Roizen and Mehmet Oz - are authors of the best-selling "You: The Owner's Manual" and "You: On a Diet." For more, go to www.RealAge.com.