Medicare's mission is to assure health care security for our beneficiaries. Title XVIII of the Social Security Act (the Act) provides the Health Care Financing Administration (HCFA) with the authority to fulfill this mission. Although Medicare is considered a defined benefit program, the Act vested Medicare with the discretionary authority to make specific policy decisions when necessary. HCFA's discretionary authority, which is found at section 1862(a)(1)(A) of the Act, enables HCFA to provide coverage for services that are reasonable and necessary for the treatment and diagnosis of illness or injury or to improve the functioning of a malformed body member. To determine whether a service is reasonable and necessary, HCFA relies on authoritative evidence. This evidence includes, but is not limited to, approvals from appropriate federal agencies, such as the Food and Drug Administration, and systematic evaluations of scientific literature via technology assessments. HCFA also may decide that a service warrants a unique type of coverage policy, which is referred to as coverage with conditions. This form of coverage is a middle ground between strict noncoverage and general coverage for a medical service that appears promising, but still is evolving. All these policy specifications effect Medicare coverage of oncology services. This means that reasonable and necessary diagnostic and therapeutic cancer-related services that are not otherwise prohibited by Medicare's statute, regulations, and manual instructions are covered and paid for by the program. Prior to the Balanced Budget Act of 1997 (BBA '97), Medicare provided coverage for some beneficiaries to undergo mammography and Papanicolaou smear screening. As a result of BBA '97, Congress has mandated expanding coverage for these services as well as adding coverage for pelvic examinations, prostate cancer screening, colorectal screening, and antiemetic drugs used as part of an anticancer chemotherapy regimen. Other specific coverage policies that relate to cancer treatment include coverage for Group C cancer drugs and off-labeled use of some drugs. HCFA is committed to providing its beneficiaries with quality health care services and will continue to monitor the progress of oncology services with an eye to establishing national policies for those services that demonstrate through authoritative evidence that they are reasonable and necessary.