114P Retrospective analysis to validate the CTS5 in patients from El Álamo IV registry and GEICAM adjuvant studies

Estimating the risk of late distant recurrence (DR) is an important goal for the management of hormone receptor-positive (HR+) early breast cancer (EBC) patients (pts) after 5 years of endocrine treatment (ET) without recurrence. The Clinical Treatment Score post–5 years (CTS5) tool was developed to estimate residual risk of Distant Recurrence (DR) after 5 years of ET (Dowsett 2018). CTS5 is a continuous score based on 4 clinical variables (number of positive nodes, tumor size, grade, and age) which distributes HR+/human epidermal growth factor receptor-negative (HER2-) EBC pts in 3 risk of DR groups depending on the score (low-risk: <3.13, intermediate-risk: 3.13-3.86 and high-risk: > 3.86). We performed a retrospective analysis of 5739 HR+/HER2- EBC pts to validate the CTS5 score as prognostic tool of late relapse, beyond 5 years. They were selected from El Álamo IV registry with pts diagnosed between 2002 and 2005 (N=3061) and 4 adjuvant GEICAM studies (9805, 9906, 2003-02 and 2003-10; N=2678) carried out from 1996 and 2006. Pts had to be distant recurrence free at 5 years from ET initiation. CTS5 classified 43.9% as low-risk, 32.2% as intermediate-risk and 23.9% as high-risk. A significant difference in DR was seen among the three groups, HR intermediate-risk vs low, 2.55 (95% CI, 1.85 to 3.52) and HR high-risk vs low, 5.77 (95% CI, 4.28 to 7.78). The continuous CTS5 (range: 1.2 - 6.06) was significantly prognostic (HR, 2.31; 95% CI, 2.05 to 2.61). DR percentage expected and observed by subgroups are described in the table. The CTS5 was able to classify Spanish patients according to different risk of late DR, independently of menopausal status, ET duration or CT treatment. However, the model seems to overestimate the number of events particularly in the high-risk group. This overestimation was more pronounced among patients treated with ET for less than 60 months or those not receiving CT.