29P Long-term performance of residual cancer burden (RCB): Clinical pathological stage (CPS) and CPS+ER+Grade (CPS-EG) models in ER+HER2- breast cancer (BC) patients (pts) after neoadjuvant chemotherapy (NAC) - Role of Ki67 drop and extended endocrine therapy (EET)

RCB, CPS and CPS-EG score are prognostic models for pts who received NAC. For CPS and CPS-EG models limited data exist beyond 5y. We evaluated the long-term performance of these models in our ER+/HER2- BC pts receiving NAC, and the impact of incorporating Ki67 drop and EET on them. Records of pts with lumB-like BC (Ki67≥20%) receiving NAC from 2008 to 2015 at our Hospital. Ki67 drop: Ki67% at surgery minus Ki67% at initial biopsy (Ki67-pre). Uni and multivariate Cox models for Distant Disease-Free Survival (DDFS) and Overall Survival (OS), concordance indexes (c-index). 5y Landmark analyses to assess the impact of ETT. Population: N = 202; median (M) age 47y (24-78); PgR:43%/20-95, Ki67-pre M/range 40/ 20-95; Histologic Grade (%) 2/3: 57/41; stage 2/3 (%): 62/38; pCR: 12%. Follow-up (M): 9.6 y. EET prescribed in 45% of pts alive without recurrence at 5y. For all pts, 10 y-DDFS (%, 95% IC) was 64% (57-72). For pts with/without pCR, 10 y-DDFS were 87% (75-100%) and 61% (53-70%), respectively (p=0.03). 10 y-DDFS and OS according to RCB, CPS and CPS+EG models are shown in the table. In DDFS, the c-index for RCB, CPS and CPS+EG were 0.70, 0.72 and 0.66, respectively for all pts and 0.69, 0.70 and 0.66, for the non-pCR cohort. Ki67 drop ≥ 20% was observed in 59% of non-pCR pts. The addition of Ki67-drop categories did not enhance the c-index of any model. EET prescription did not improve DDFS but was associated to a higher 5y OS: 89% (95% CI 81-98%) vs 68 % (95% CI 58- 81%), p < 0.01.Table: 29PPrognostic modelNDDFS HR IC 95%p valueOS HR IC 95%p valueRCB026 (17%)116 (11%)1.1 (0.19-6.6)0.910.62 (0.06-6)0.68274 (48%)1.7 (0.48-5.77)0.431.37 (0.38-4.95)0.63336 (24%)5.1 (1.48-17.4)< 0.014.8 (1.36-16.4)0.01CPS043 (22%)143 (22%)3.4 (1.1-11)0.03271 (36%)3.9 (1.33-11.2)0.012.12 (1.01-4.46)0.05335 (17%)9.5 (3.25-27.7)< 0.015.9 (2.88-12.4)< 0.0146 (3%)55 (14.87-206.7)< 0.0122.6 (8.09-63.4)< 0.01CPS+EG011 (8%)128 (20%)0.2 (0.02-2.1)0.18246 (33%)1.2 (0.26-5.5)0.81335 (25%)2.6 (0.59-11.4)0.213.63 (1.59-8.3)< 0.01419 (13%)3.5 (0.75-16)0.114.8 (1.95-11.8)< 0.0152 (1%)44.3 (5.7-343.4)< 0.0128.8 (6.08-136.3)< 0.01 Open table in a new tab In our luminal B-like BC pts, both CPS and CPS-EG models showed comparable long-term prognostic value, surpassing RCB. EET correlated with improved OS. Integrating Ki67 drop categories didn't enhance model performance, though limited numbers prevent definitive conclusions.