The original Medicare plan has more geographic flexibility than the private plan alternatives. (First of all, consider carefully when choosing a plan.) If you need help changing plans after a diagnosis, try calling the Medicare Rights Center (medicarerights.org or [800] 333-4114), a national consumer organization that provides counseling about Medicare. "Sometimes our advocates have been able to help people get off the private plan and back on original Medicare," says Paul Precht, director for policy and communications at the center. "But it's getting harder."

Be realistic.

Don't think you can find a cutting-edge technique developed by one surgeon, then ask your own doctor to do it. "That's like going to a restaurant with a recipe from another restaurant and asking the kitchen to make it," Adler says. You could ask the doctor who developed the procedure if he or she has trained any others. If so, find out where they are practicing, and how experienced they have become. That process of training others, and having them fan out, is how once-unique techniques spread across the country, but it takes a lot of time.

Be prepared to fight.

Use the ammunition you've accumulated through research. Fights with insurance companies can be frustrating and drawn out, so if you're also fighting disease, you might need to enlist a spouse or friends to make phone calls and write letters, to the insurer, to legal aid societies or to a private lawyer.

If you're wrangling with Medicare, the Medicare Rights Center might be able to help fight a denial.

Get your doctor's support.

Whether you're facing Medicare or an insurance company, your chosen doctor is your best ally. He or she is the one best armed with numbers to make your case to the insurer.

For example, surgeons at Johns Hopkins Medical Center published a study in 1995 of a surgical technique, called a Whipple procedure, that can help some pancreatic cancer patients. The study examined all 501 cases of pancreatic cancer in which the procedure was used between 1988 to 1993 throughout Maryland.

It found that 54% of Whipple procedures were performed at Johns Hopkins Medical Center. The remainder were performed at 38 other hospitals throughout the state. The in-hospital death rate at Hopkins was 2.2%, compared with an average of 13.5% at the other hospitals. But what probably got the attention of insurance companies was that the cost at Johns Hopkins was $26,204, compared with an average of $31,659 at other hospitals.

Even if there isn't such incontrovertible, published proof supporting your decision, your chosen physician will likely have other numbers.

If you lose the fight and continue to be convinced that where you go matters to you, be prepared to shell out.

Whether it's a higher co-payment for going out of network, or taking on the entire cost yourself if you can afford it, your preference may be important enough to you to pull out your checkbook or credit card.