Nottingham prognostic x (NPx): a risk stratification tool in ER‐positive HER2‐negative breast cancer: a validation study

Aims In this study, we validate the use of Nottingham Prognostic x (NPx), consisting of tumour size, tumour grade, progesterone receptor (PR) and Ki67 in luminal BC. Materials and methods Two large cohorts of luminal early‐stage BC (n = 2864) were included. PR and Ki67 expression were assessed using full‐face resection samples using immunohistochemistry. NPx was calculated and correlated with clinical variables and outcome, together with Oncotype DX recurrence score (RS), that is frequently used as a risk stratifier in luminal BC. Results In the whole cohort, 38% of patients were classified as high risk using NPx which showed significant association with parameters characteristics of aggressive tumour behaviour and shorter survival (P