Determining the number of primary tumors is:

• A. Important if registry data are to be comparable
• B. Is the same in the United States and worldwide
• C. Neither a nor b
• D. Both a and b

Answer: (A)

Determining the number of primary tumors is about making sure cancer registry data are comparable across different programs. Counting each distinct primary tumor, when done with consistent rules about what counts as a new primary, lets incidence rates and trends be meaningfully compared from one registry to another. In practice, guidelines differ on when a new tumor in the same person is considered a separate primary, or how to handle multiple primaries in the same or different sites, so data are not identical worldwide. That’s why this is about achieving comparability, not about universal sameness.