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Anastrozole is cost-effective vs tamoxifen as initial adjuvant therapy in early breast cancer: Canadian perspectives on the ATAC completed-treatment analysis

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Abstract

Goals of work

To conduct an economic analysis comparing tamoxifen and anastrozole (Arimidex) in the adjuvant treatment of hormone receptor-positive (HR+), post-menopausal early breast cancer patients.

Materials and methods

An economic model examined typical patients (64 years of age, HR+, 64% node negative) from the Arimidex, tamoxifen alone, or in combination (ATAC) trial over a lifetime horizon. Rates of events were derived from ATAC trial results. Post-trial event rates were drawn from the literature for tamoxifen; event rates for anastrozole were modified by the relative risks observed in the ATAC trial. Resource utilization was drawn from Statistics Canada’s Population Health Model for breast cancer, supplemented by an expert panel. A public health care system perspective, 2004 Canadian prices and a 5% discount rate were employed.

Results

Anastrozole-taking patients incurred additional hormonal treatment costs compared to tamoxifen-taking patients (incremental lifetime cost, CDN$6,974 per patient), partially offset by reduced downstream recurrences of breast cancer (CDN$1,143 lifetime savings per patient) for a net incremental cost of CDN$5,796 per patient on anastrozole. The anastrozole-treated patients were projected to experience a 5.6% absolute risk reduction of first breast cancer recurrence and a 2.8% absolute risk reduction in breast cancer death. This corresponded to CDN$30,000 per life year gained and CDN$28,000 per quality-adjusted life year gained (95% confidence interval, $17,428 to $54,605). The results were affected by the duration and extent of anastrozole benefit under sensitivity analysis but remained cost-effective.

Conclusion

Compared to tamoxifen, anastrozole therapy is effective and cost-effective as initial adjuvant therapy in post-menopausal, HR+ early breast cancer patients.

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Acknowledgements

The authors wish to thank Dr. Jean-Marie Berthelot (Statistics Canada) and Dr. Ivo Olivotto (British Columbia Cancer Agency) for their generous sharing of data. This research was partially supported by an unrestricted grant from AstraZeneca Canada

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Authors and Affiliations

  1. Axia Research, 181 Main Street West, Hamilton, L8P 4S1, Canada

    A. Rocchi

  2. Ottawa Regional Cancer Center, 501 Smyth Road, Ottawa, Canada

    S. Verma

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Correspondence to A. Rocchi.

Appendix

Appendix

Summary of major clinical assumptions

  • It was assumed that hormonal therapy was administered for five years, unless patients discontinued therapy.

  • It was assumed that all recurrences and deaths occurred at the mid-point of a year.

  • The rate of first recurrence for tamoxifen, years six to ten, was assumed to be the rate reported by the EBCTCG, for trials with five year intended duration, weighted by nodal status.

  • The rate of first recurrence for anastrozole, years six to ten, was assumed to be the tamoxifen first recurrence rate, modified by the hazard ratio.

  • The rate of first recurrence for tamoxifen, years eleven to fifteen, was assumed to be the mean tamoxifen rate for years six to ten.

  • The rate of first recurrence for anastrozole, years eleven to fifteen, was assumed to be the mean tamoxifen rate for years six to ten.

  • The rate of first recurrence for tamoxifen or anastrozole, years fifteen to thirty-five, was assumed to be that of the general population.

  • The distribution by type of first recurrences, years six to fifteen for tamoxifen, was assumed to follow the ATAC distribution for tamoxifen, years one to five (LRR:DR:CO=25%:60%:15%).

  • The distribution by type of first recurrences, years six to ten for anastrozole, was assumed to follow the ATAC distribution for anastrozole, years one to five (LRR:DR:CO=25%:66%:9%).

  • The distribution by type of first recurrences, years eleven to fifteen for anastrozole, was assumed to follow the ATAC distribution for tamoxifen, years one to five (LRR:DR:CO=25%:60%:15%).

  • The occurrence of DR subsequent to LRR, years six to fifteen, was assumed to be 58%, three years after the LRR.

  • The occurrence of DR subsequent to CO, years six to fifteen, was assumed to be 58%, three years after the CO.

  • Mortality due to breast cancer, years six to fifteen, was assumed to occur only in women with DR, and the mortality rates were those of the BC database rates for Stage IV breast cancer.

  • Mortality due to breast cancer, years sixteen to thirty-five, was assumed to be accounted for by deaths from other causes.

  • Mortality due to adverse events, years one to thirty-five, was assumed to be accounted for by deaths from other causes.

  • It was assumed that adverse events due to hormonal therapy terminated with the discontinuation of hormonal therapy at five years.

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Rocchi, A., Verma, S. Anastrozole is cost-effective vs tamoxifen as initial adjuvant therapy in early breast cancer: Canadian perspectives on the ATAC completed-treatment analysis. Support Care Cancer 14, 917–927 (2006). https://doi.org/10.1007/s00520-006-0035-8

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