Early implementation of radiofrequency ablation for breast cancer in Japan: what national claims data reveal and obscure.

Japan introduced national health insurance coverage for radiofrequency ablation (RFA) in selected patients with early breast cancer on 1 December 2023. We used public aggregate claims data to determine which features of early implementation were observable and which were obscured by disclosure controls. We analyzed the 10th and 11th releases of open data from Japan's National Database of Health Insurance Claims and Specific Health Checkups (NDB Open Data). Breast RFA was identified by procedure code 150444250 (K476-5 in fiscal year 2024). A matching row was found only in inpatient sheets. Fiscal year 2024 contained 376 claim-recorded procedure occurrences. All sex-by-age occurrences were tabulated in female strata. Disclosed age cells for ages 40-84 years accounted for 362 occurrences (96.3%); suppressed female cells for ages 25-39 and 85-89 years accounted for the residual 14 (3.7%). Disclosed prefectural counts summed to 320 (85.1%), whereas 56 occurrences (14.9%) remained unallocated because 20 prefectural cells were suppressed. Monthly counts ranged from 17 to 52. Including public-expense-only claims increased the annual total from 376 to 379. Public aggregate claims provided a national inpatient billing benchmark and limited age profile but could not fully characterize geographic implementation, identify unique patients, or assess appropriateness or outcomes. Post-reimbursement surveillance should use claims and clinical registries as complementary data sources, with aligned observation periods, procedure definitions, and counting units.