Real-World Experience Using the Clinical Treatment Score at 5 Years (CTS5) and Breast Cancer Index (BCI) to Guide Extended Adjuvant Endocrine Therapy
Abstract
Background: Accurately identifying patients with estrogen receptor-positive (ER+), HER2-negative breast cancer benefiting from extended endocrine therapy (EET) remains challenging. While the Clinical Treatment Score at 5 yrs (CTS5) and the Breast Cancer Index (BCI) are established tools for assessing late recurrence risk, their comparative utility in real-world practice is under-explored. CTS5 provides prognostic data only and BCI) provides both prognostic and predictive data.
Methods: We conducted a retrospective study evaluating concordance between CTS5 and BCI in early-stage ER+, HER2-negative patients who completed five years of adjuvant endocrine therapy (2023–2024). Inter-test reliability was quantified using descriptive statistics and Cohen’s kappa.
Results: In 59 patients, overall concordance was 37.3%. Agreement was highest in low-risk, grade 1 tumors (54.5%). Discordance was significant in those with higher-risk features. Notably, 32.2% were CTS5 "intermediate," where BCI offered binary guidance. Sankey diagrams revealed 57.1% of BCI-recommended EET patients were CTS5 low-risk. Cohen’s kappa was 0.067 (95% CI [-0.156, 0.29], p=0.559).
Conclusion: Our study showed limited CTS5 and BCI concordance rates in clearly low-risk populations and non-statistically significant results overall. These limited findings warrant further exploration of integrating genomic assays to optimize therapy duration.
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