The National Institute for Health and Care Excellence (NICE) invited the manufacturer of pertuzumab (Roche) to submit evidence for the clinical and cost effectiveness of pertuzumab + trastuzumab + docetaxel for the treatment of human epidermal growth factor receptor 2-positive (HER2+) metastatic or locally recurrent unresectable breast cancer in accordance with the Institute’s Single Technology Appraisal (STA) process. The Liverpool Reviews and Implementation Group (LRiG) at the University of Liverpool was commissioned to act as the Evidence Review Group (ERG). This article summarises the ERG’s review of the evidence submitted by the manufacturer and provides a summary of the Appraisal Committee’s (AC) initial decision. At the time of writing, final guidance had not been published by NICE. The clinical evidence was mainly derived from an ongoing phase III randomised double-blind placebo-controlled international multicentre clinical trial (CLEOPATRA), designed to evaluate efficacy and safety in 808 patients, which compared pertuzumab + trastuzumab + docetaxel (pertuzumab arm) with placebo + trastuzumab + docetaxel (control arm). Both progression-free survival (PFS) and overall survival (OS) were analysed at two data cut-off points—May 2011 (median follow-up of 18 months) and May 2012 (median follow-up of 30 months). At both time points, PFS was significantly longer in the pertuzumab arm (18.5 months compared with 12.4 months in the control arm at the first data cut-off point and 18.7 versus 12.4 months at the second data cut-off point). Assessment of OS benefit suggested an improvement for patients in the pertuzumab arm with a strong trend towards an OS benefit at the second data cut-off point; however, due to the immaturity of the OS data, the magnitude of the OS benefit was uncertain. Importantly, cardiotoxicity was not increased in patients treated with a combination of pertuzumab + trastuzumab + docetaxel. The ERG’s main concern with the clinical effectiveness data was the lack of mature OS data. An additional concern of the AC was that the majority of patients in the randomised controlled trial were trastuzumab naïve, which does not reflect current clinical practice. The incremental cost-effectiveness ratios (ICERs) generated by the manufacturer’s model are considered to be commercial in confidence data and therefore cannot be published. Nevertheless, the results of the manufacturer’s probabilistic sensitivity analyses suggest that pertuzumab + trastuzumab + docetaxel has a 0 % probability of being cost effective at a willingness-to-pay of £30,000 per quality-adjusted life-year gained when compared with trastuzumab + docetaxel. The ERG believes that more realistic estimates of the ICERs are considerably higher, almost double those presented by the manufacturer. This is because the ERG believes that due to the manner in which the economic model is constructed, the additional survival benefit following disease progression that is generated for patients treated with pemetrexed + trastuzumab + docetaxel is unrealistic. At the time of writing, NICE had not made a final decision regarding this technology but had instead referred the issue of the assessment of technologies that are not effective at a zero price to their Decision Support Unit for advice.