Real-World Experience Using the Clinical Treatment Score at 5 Years (CTS5) and Breast Cancer Index (BCI) to Guide Extended Adjuvant Endocrine Therapy BCI vs. CTS5
Abstract
Background: Accurately identifying patients with estrogen receptor (ER)+HER2− breast cancer benefiting from extended endocrine therapy (EET) remains challenging. While the Clinical Treatment Score at 5 Years (CTS5) and the Breast Cancer Index (BCI) are established tools for assessing late recurrence risk, their comparative utility in real-world practice is underexplored. The CTS5 only provides prognostic data, but the BCI provides both prognostic and predictive data.
Methods: We conducted a retrospective study evaluating concordance between the CTS5 and the BCI in patients with early-stage ER+HER2− disease who completed 5 years of adjuvant endocrine therapy (2023–2024). Intertest reliability was quantified using descriptive statistics and the Cohen κ coefficient.
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 the BCI offered binary guidance. Sankey diagrams revealed that 57.1% of patients with BCI-recommended EET were CTS5 low risk. The Cohen κ coefficient was 0.067 (95% CI, −0.156 to 0.290; P = 0.56).
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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