The 21-gene recurrence score (RS) predicts the benefit of adjuvant chemotherapy (CT) in ER-positive, HER2-negative breast cancer (BC) and has been validated in a population where women under 40 are underrepresented. Young BC pts are more likely to receive adjuvant chemotherapy (CT) in addition to endocrine therapy (ET). Our objective was to assess the RS results in young (≤40 yo) vs older (>40 yo) pts and evaluate the impact of age on clinical decision making according to RS categories.
We retrospectively reviewed electronic medical files of all patients with early stage hormone receptor BC for whom RS was available between 2007 and 2017 in 3 specialized cancer centers. We used the Mann-Whitney and Chi-squared tests to assess differences between age group. Similarly, we evaluated the association between age groups and treatment, within each ODx category. To determine if age was associated with CT use in the low-risk category, a logistic regression model was constructed.
A total of 551 pts were included, 53 (9.6%) ≤40 yo and 498 (90.4%) >40 yo. No statistical differences were found between the younger and older groups in T (p = 0.874), N (p = 0.794), stage (p = 0.188), or grade (p = 0.791). Young patients underwent radical surgery more frequently than their older counterparts (41.5% vs 25.7%, p = 0.014). Statistically significant differences were also observed in ER mean, which was lower in the younger group (80% vs 90%, p < 0.001). The median RS result was significantly higher in the younger group (19 vs 16, p = 0.009). Also, high-risk recurrence score category was significantly more frequent in the younger group (22.6% vs 9.2%, p = 0.009). In the intermediate-risk category there were no differences in the proportion of patients who received CT according to age groups (p = 0.484). In the low-risk category, 28.0% of patients ≤40 years vs 11.3% of patients >40 years received CT (p = 0.037).
Our results indicate that RS tends to be higher in patients with BC ≤ 40 yo and that the frequency of high-risk RS is significantly higher in the younger group, suggesting biological differences between groups. 28% of young patients with low-risk RS from our cohort are overtreated. Based on these results, it should be considered to develop a test adjusted to the age of the patients.
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