KLP-PI: a new prognostic index for luminal B HER-2-negative breast cancer

Luminal B HER-2-negative (LBHN) subtype is one of the major subtypes of breast cancer according to different features, clinical behaviors, and treatment response. The LBHN subtype shows a poor prognosis and is insensitive to endocrine therapy. Our work aim is to investigate the prognostic factor in the LBHN subgroup and, meanwhile, try to obtain an optimal prognostic index (PI) contrapose LBHN subgroup which helps to guide chemotherapy. A total of 515 female LBNH patients who underwent diagnosis and surgery at our hospitals from August 2008 to August 2018 were enrolled. Clinical-pathological information was obtained and immunohistochemistry result was available. From these cases, a 30% Ki-67 LI was employed to divide LBHN into two groups with low and high levels; high Ki-67 LI was associated with GIII tumor grade (P < 0.001), positive axillary lymph nodes (ALN) status (P = 0.018) and negative PR status (P = 0.016), and also seemed to be related to T2-T3 tumor size (P = 0.058). High Ki-67 level (HR = 3.30; P < 0.011), positive ALN (HR = 7.29; P < 0.001) and PR negative (HR = 2.63; P = 0.034) significantly associated with poor 5-year DFS in multivariate Cox's proportional hazard regression model. A novel prognosis prediction model (KLP-PI), based on Ki-67 LI, ALN and PR status, showed a better discriminatory ability compared with traditional Nottingham prognostic index targeted to LBHN breast cancer. Our study highlights that high Ki-67 LI, positive ALN and negative PR status were associated with poor outcome in LBHN patients, and composed by these prognostic factors, KLP-PI improves the prognostic assessment using the Nottingham Prognostic Index when aiming at LBHN subtype.