Older cancer patients in the U.S. often face high out-of-pocket costs that are a significant financial burden, according to a new study.

Medicare, the federal health insurance program for the elderly and disabled, establishes the fees doctors and hospitals are allowed to charge Medicare patients - but then generally only pays 80 percent of those fees.

Patients are left to cover the remaining 20 percent. Many people enroll in Medicare HMOs, or they buy so-called Medicare supplemental policies, to help cover the gap.