Cost-effectiveness of switching to exemestane versus continued tamoxifen as adjuvant therapy for postmenopausal women with primary breast cancer

Background. Sequential tamoxifen/exemestane therapy reportedly improves disease-free survival in women with primary breast cancer compared with continued tamoxifen therapy. The objective of the current study was to assess the cost-effectiveness of switching to exemestane after 2 to 3 years of tamoxifen versus continued tamoxifen in postmenopausal women with primary breast cancer for a total of 5 years of adjuvant therapy. Methods. A Markov model based on the Intergroup Exemestane Study (IES) population compared switching to exemestane versus continued tamoxifen for 2.5 years of therapy and 5 years of postadjuvant therapy follow-up. Disease progression and hazards ratios (HR) for recurrence and survival were determined from datasets (IES and the Surveillance, Epidemiology, and End Results program of the National Cancer Institute) and from the published literature. An expert panel validated treatment patterns, outcomes, and resource utilization. Direct medical costs were included based on published sources. Cost-effectiveness ratios were determined, and extensive sensitivity analyses were conducted. Results. Exemestane was found to be more effective than tamoxifen alone with regard to disease-free survival (2.6% absolute improvement), life-years gained (0.1028 LY), and quality- adjusted life-years gained (0.1195 QALY), at an additional cost of Can$2889 per person over 7.5 years. Incremental cost-effectiveness ratios were Can$28,119/LY gained and Can$24,185/QALY gained. The model was most sensitive to distant recurrence HR but was robust to variations in clinical, cost, and utility parameters. Conclusions. Switching to adjuvant exemestane after 2 to 3 years of tamoxifen is cost-effective in postmenopausal women with primary breast cancer.