The analysis was based on a Markov model using a hypothetical cohort of 1,000 postmenopausal women (mean age 64 years) postmenopausal women with HR-positive early stage breast cancer who had completed primary therapy. The time horizon of the study was the lifetime of the patient. The authors reported that a societal perspective was used, but stated that only direct medical costs were included.
Clinical and effectiveness data came from previously published studies. The main measures of effectiveness used were disease-free survival, recurrence rates, and occurrence of adverse events. These data came from the Arimidex, Tamoxifen, Alone or in Combination (ATAC) large randomised controlled trial (Cuzick 2010, see Other Publications of Related Interest) which had median follow-up of 10-years.
Monetary benefit and utility valuations:
Utility estimates for each health state in the model were elicited through an interview of 20 experienced oncology nurses (from the National Cancer Centre in Singapore), where each nurse rated patients using the Visual Analogue Scale (VAS).
Measure of benefit:
Life-years and quality-adjusted life-years (QALYs) were the summary benefit measures. Future benefits were discounted using an annual rate of 3%.
The direct costs included: trial medications; other medications; doctor consultations; laboratory tests and scans; treatment of recurrences; and treatment of adverse events, including endometrial cancer, ischaemic events, spine fractures and venous thromboembolic events. Resource use came from a retrospective review of the medical records of postmenopausal HR-positive early stage breast cancer patients treated at the Singapore National Cancer Centre with anastrozole or tamoxifen adjuvant therapy from 2001 to 2009. Costs were obtained from the financial department of the Singapore National Cancer Centre and another hospital. All costs were inflated to 2010 prices using the healthcare component of the consumer price index. Future costs were discounted using an annual rate of 3%. Costs were reported in Singapore dollars (SGD).
Analysis of uncertainty:
One-way and multi-way sensitivity analyses were conducted by varying the values of key parameters including the recurrence rates, adverse event rates, treatment costs, utility scores, and discount rates.