The 21-Gene Recurrence Score Assay

Between 2001–2003 Paik and others, from a US-based multiinstitutional clinical trials group (the NSABP) that includes many Canadian centres, developed an assay to identify 21 genes from tumour samples that collectively significantly predicted patients’ outcomes (recurrences, breast cancer deaths, and response to chemotherapy).1 The 21-gene assay was based on advances in genetic techniques, refining the molecular significance of related genes to produce a “portrait” of tumour or “tumour signature” reflecting tumour biology and risk of relapse.2, 3 An algorithm was developed defining a Recurrence Score (RS) based on the various constellations of the 21 genes isolated from the tumour sample. RS was expressed as low (RS<18), medium (RS=18-30), or high (RS>31). Overall, it was shown that among node negative breast cancer patients with positive estrogen receptors, 51 per cent had a low RS, 22 per cent a medium, and 27 per cent a high RS. More recently, data became available for node positive patients, and among those, close to 40 per cent had low RS (Albain et al.7). According to the 2004 pivotal analysis, if the RS was low, patients relapsed significantly less often than patients with intermediate or high RS. The rates of distant recurrence at 10 years were respectively 6.8 percent, 14.3 percent, and 30.5 per cent.