BACKGROUND:In a phase III trial of women with HER2+ metastatic breast cancer (MBC) previously treated with trastuzumab, an anthracycline, and taxanes (EGF100151), lapatinib plus capecitabine (L+C) improved time to progression (TTP) versus capecitabine monotherapy (C-only). In a trial including HER2+ MBC patients who had received at least one prior course of trastuzumab and no more than one prior course of palliative chemotherapy (GBG 26/BIG 03-05), continued trastuzumab plus capecitabine (T+C) also improved TTP.METHODS:An economic model using patient-level data from EGF100151 and published results of GBG 26/BIG 03-05 as well as other literature were used to evaluate the incremental cost per quality-adjusted life-year [QALY] gained with L+C versus C-only and versus T+C in women with HER2+ MBC previously treated with trastuzumab from the UK National Health Service (NHS) perspective.RESULTS:Expected costs were £28,816 with L+C, £13,985 with C-only and £28,924 with T+C. Corresponding QALYs were 0.927, 0.737 and 0.896. In the base case, L+C was estimated to provide more QALYs at a lower cost compared with T+C; cost per QALY gained was £77,993 with L+C versus C-only. In pairwise probabilistic sensitivity analyses, the probability that L+C is preferred to C-only was 0.03 given a threshold of £30,000. The probability that L+C is preferred to T+C was 0.54 regardless of the threshold.CONCLUSIONS:When compared against capecitabine alone, the addition of lapatinib has a cost-effectiveness ratio exceeding the threshold normally used by NICE. Compared with T+C, L+C is dominant in the base case and approximately equally likely to be cost-effective in probabilistic sensitivity analyses over a wide range of threshold values.