PGR and ductal breast carcinoma in situ: During the development and validation of the 21-gene assay, several clinicopathological characteristics were found to correlate with the 21-gene RS: younger age, higher tumour grade and lower PR expression were correlated with higher RS results.10,17,18 In addition to these previous findings, our study discovered that the DCIS component in IDC also impacted the 21-gene RS, as concomitant DCIS in IDC was independently related to lower 21-gene RS, which may be due to the relatively better biological behaviour in IDC patients with the DCIS component.