Further multivariate analysis showed that younger age (P < 0.001), larger tumour (P = 0.010), positive node (P < 0.001), higher IDC grade (P < 0.001), lower PR expression (P < 0.001), higher Ki67 (P < 0.001) and higher 21-gene RS (P < 0.001) were independent predictive factors for chemotherapy recommendation (Supplementary Table 3). Here, PGR is linked to neoplasm.