To investigate the correlation between the 21-gene recurrence score (RS)and clinicopathological characteristics of women with hormone receptor(HR)-positive, HER-2-negative breast cancer, and RS distribution in patients with different body mass index(BMI)and to explore the clinical significance of RS in the personalized treatment of breast cancer patients.

The clinicopathological data of 142 female patients with HR-positive, HER-2-negative breast cancer, which were surgically resected and pathologically confirmed in the Third Affiliated Hospital of Soochow University from September 2017 to August 2021, were retrospectively analyzed. The expression of 21 genes was detected by real-time fluorescence quantitative polymerase chain reaction and RS was calculated. According to RS, patients were divided into three subgroups: low (RS≤15), medium (15<RS<26), and high RS (RS≥26); According to BMI, patients were divided into three subgroups: normal weight group (BMI<24.0 kg/m²), overweight(24.0 kg/m²≤BMI<28.0 kg/m²), and obese group (BMI≥28 kg/m²). χ² test or Fisher’s exact test was used to compare the clinicopathological characteristics among different RS groups and different BMI groups. The linear correlation analysis was conducted on continuous variables with statistical significance. Because of skewed distribution, RS was expressed as M (P₂₅, P₇₅), and compared using nonparametric rank sum test between groups. The nonparametric rank sum test was used for graded data (histological grades). The McNemar test was used to compare the traditional postoperative recurrence risk grouping and 21-gene RS grouping.

According to RS, patients were divided into low (n=105), medium (n=21) and high RS group (n=16), and according to BMI, patients were divided into normal weight group (n=83), overweight (n=48) and obese group (n=11). Statistically significant differences were found in the tissue grade(H=13.824, P=0.001), PR expression(χ²=18.884, P<0.001), Ki-67(χ²=15.483, P<0.001)and molecular typing (χ²=12.986, P=0.002)among different RS groups. Further analysis showed that RS was negatively correlated with PR expression (r=-0.520, P<0.001)and positively correlated with Ki-67(r=0.487, P<0.001). Statistically significant differences were found in the age(χ²=8.401, P=0.015)and menopausal status(χ²=9.060, P=0.011)among different BMI groups. No significant difference was found in RS value(H=0.460, P=0.795)and its distribution(χ²=3.042, P=0.537)among normal weight group, overweight group and obese group. There was a significant difference between the RS grouping and the traditional postoperative recurrence risk grouping(χ²=55.850, P<0.001). Only 19 out of 72 patients were reclassified as low recurrence risk group according to 21-gene RS from intermediate traditional postoperative recurrence risk group and received adjuvant chemotherapy. The postoperative follow-up period was 7.0-54.0 months (median: 22.5 months). Until March 2022, no recurrence or disease progression was observed.

The 21-gene RS could provide a reference for the adjuvant chemotherapy of patients with early HR-positive, HER-2-negative breast cancer.