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

Abstract

Background: Identifying high-risk of late recurrence (beyond 10 years) in patients with hormone receptor-positive HER2-negative early breast cancer (EBC) is crucial. The Clinical Treatment Score post-5 years (CTS5) score assesses recurrence risk after 5 years of endocrine therapy (ET). This study validated CTS5 as a prognostic tool for late recurrence by examining its association with Distant Recurrence-Free Survival using GEICAM study data and evaluating model calibration.

Patients and methods: We retrospectively analyzed 5739 hormone receptor-positive HER2-negative EBC patients from the El Álamo IV registry (N = 3509, diagnosed between 2002 and 2005) and 4 adjuvant GEICAM studies (N = 2680, conducted between 1996 and 2006). All patients were distant recurrence-free and alive 5 years after starting adjuvant ET.

Results: The CTS5 classified 43.9% of patients as low-risk, 32.2% as intermediate-risk, and 23.9% as high-risk. Significant differences in DR were observed: hazard ratio (HR) for intermediate- vs. low-risk was 2.55 (95% CI, 1.85-3.51, P < .0001), and HR for high- vs. low-risk was 5.77 (95% CI, 4.28-7.78, P < .0001). Similar results were found across subgroups by menopausal status, duration of adjuvant ET, and prior adjuvant chemotherapy (CT). Calibration showed CTS5 overestimated DR rates in low-risk (P = .0314) and high-risk (P < .0001) patients compared to observed rates.

Conclusions: The CTS5 categorized patients based on late DR risk regardless of menopausal status, ET duration, or CT treatment. However, the model tended to overestimate events, particularly in high-risk groups, especially among those treated with ET for less than 60 months or not receiving CT.