Discrepancy in risk assessment of hormone receptor positive early-stage breast cancer patients using breast cancer index and recurrence score

Purpose: A recent comparison of the prognostic accuracy of Breast Cancer Index (BCI) and the Recurrence Score (RS) showed that BCI was more precise than RS. BCI identified a subset of RS low and intermediate risk patients with clinically relevant elevated rates of distant recurrences (DR). The current study analyzed the correlation of BCI and RS risk classification to clinical and pathological parameters and further examined the re-categorization between the two risk group indices in a multi-institutional cohort of hormone receptor positive (HR+) breast cancer patients. Methods: 560 women with HR+, lymph node-negative breast cancer who underwent testing with RS as part of their routine clinical care were included in the final analysis. Individual risk was assessed using predefined categories of RS and BCI (Low, Intermediate and High, respectively). Correlations between BCI, RS, and standard clinical-pathological prognostic factors were examined, and re-categorization of risk groups between BCI and RS was analyzed. Results: An overall significant association between histological tumor grade and RS or BCI was observed with high-grade tumors more prevalent among RS and BCI high-risk patients. The invasive ductal carcinoma histologic subtype was associated with 98% and 93% of high-risk RS and BCI cases, respectively. The invasive lobular subtype accounted for 0% and 6% of high-risk RS and BCI cases, respectively. A poor agreement between the two biomarker risk group indices was demonstrated with more than 51% of the total cohort stratified differently between BCI and RS. As compared with RS, BCI stratified fewer patients into the intermediate-risk group (29% vs. 39%, BCI and RS, respectively) and more patients into the high-risk group (19% vs. 7%, BCI and RS, respectively). Subsets of both RS low- and intermediate-risk patients were identified by BCI as high risk. Conclusions: In this clinical series, BCI and RS risk groups demonstrated a significant association with histological tumor grade. BCI showed a modest correlation with tumor size and no correlation with age, while RS showed no correlation with tumor size or age. Compared with RS, BCI classifies fewer intermediate risk patients, identifies subsets of low and intermediate RS risk patients as high-risk, and provides distinct individualized risk assessment for patients with early-stage breast cancer.