Model parameters and assumptions
| Parameter | Description | Source data and assumptions |
|---|---|---|
| Breast cancer screening and diagnosis | ||
| Screening utilization rates | Biennial screening exams for new screening participants, assuming 100% return rates over 25 years | Maximum additional costs and the average age of new mammography screening participants |
| Abnormal index exam rate | Percentage of index mammograms identified as abnormal; 19.5% of all index exams | Screening cohort, index exam |
| Subsequent abnormal exam rate | Probability of a subsequent abnormal exam; 9.0% | Screening cohort, subsequent exams |
| Detection after an abnormal exam | Time-dependent rate of developing breast cancer following history of any abnormal exam result | Screening cohort linked with breast cancer cohort |
| Incremental cancer detection rate | Additional incidences of low-risk breast cancer applied to the intervention arm attributed to increased cancer detection rates from DBT plus DM over DM alone (an additional 1.6 per 1000), applied biennially over 25 years | Parameter assumption based on meta-analysis (18) |
| Undetected breast cancer | Time-dependent rate of developing breast cancer in the absence of any abnormal exam result, by high- or low-risk breast cancer | Screening cohort linked with breast cancer cohort |
| Absolute recall rate reduction | Absolute recall rate reduction from meta-analysis of observational trials for the use of DBT versus DM (2.2%), applied biennially over 25 years | Parameter assumption based on meta-analysis (18) |
| Mortality | ||
| Survival | Long-term survival for ever-screened participants, after diagnosis, by high- or low-risk breast cancer | Breast cancer cohort |
| Background mortality | Age- and sex-specific mortality adjustments by 5-year age groupings | Statistics Canada data for female mortality by age, in BC |
| Costs | ||
| Screening | $125 for DM; $169 for combined DM and DBT, applied biennially, over 25 years | Established billing fees for Alberta Health Services* |
| Diagnostic evaluation | $550 following the first abnormal exam | Mean cost for investigation in BC* |
| Treatment costs | Health state–specific costs, in 2019 Canadian dollars | Resource utilization rates and unit costs for screening participants who had breast cancer |
| Utilities | ||
| Screening with normal exam results | Quality of life expected for screening with normal exam results, 0.006 decrease in utility score for 1 week after having a mammogram (0.994) | Matched CISNET assumption† |
| Screening with an abnormal exam result | Quality of life following an abnormal exam result. Year 1, utility = 0.990 (5 wk of disutility); years 2–40 returns to 1.000 | CISNET assumptions for false positive exams† |
| Low-risk breast cancer | Utility weight of 0.900 for 2 years, then returns to 1.000 | CISNET assumptions for localized breast cancer and expert opinion† |
| High-risk breast cancer | Utility weight of 0.750 for the first 13 years, then 0.600 for years 14–40. | CISNET assumptions for advanced breast cancer and expert opinion† |
Note: CISNET = National Cancer Institute’s Cancer Intervention and Surveillance Modeling Network, DBT = digital breast tomosynthesis, DM = digital mammography.
↵* Unit costing described in full detail in Appendix 1, available at www.cmajopen.ca/content/9/2/E443/suppl/DC1.
↵† Common model inputs used by the CISNET modelling group and consensus with the breast cancer experts on this study team (C.L. and C.M.). (28)