Supplementary Material for: Circulating glypican-4 is a predictor of 24-month overall survival in metastatic breast cancer

Background & objective: Endocrine treatment combined with CDK4/6 inhibitors is the preferred treatment strategy in patients presenting with ER-positive/HER2-negative breast cancer, but the clinical course remains highly variable among individual patients. There is an unmet need for prognostic or predictive biomarkers in this important group of patients. Recently, we have identified circulating glypican-4 (GPC4) as a new biomarker of inferior outcomes in patients with metastatic colorectal cancer. The impact of plasma GPC4 levels on the survival of breast cancer patients is unknown and has been addressed in the present study. Methods: Our study included 47 patients with ER-positive/HER2-negative metastatic breast cancer prior to treatment with CDK4/6 inhibitors combined with endocrine therapy. The endpoint was overall survival (OS) at 24 months. GPC4 levels were measured in plasma using an enzyme-linked immunosorbent assay. Results: Increased circulating GPC4 levels were significantly linked to advanced age, postmenopausal state, visceral metastases, and invasive lobular carcinoma. During the two-year observational follow-up period, 25.5 % of patients died. The area under the receiver operating characteristic curve (ROC-AUC) analysis revealed an AUC of 0.713 [0.555-0.871]; P=0.029 for OS and an optimal cut-off value of GPC4 for predicting OS of 4.77 ng/mL. No patient showing GPC4 values below this cut-off died during the observational period. Cox regression analysis showed a hazard ratio of 2.14 [95% confidence interval: 1.24-3.67]; P=0.006 for one standard deviation change of plasma GPC4. Conclusions: In conclusion, our study suggests circulating GPC4 as a significant predictor of poor survival in metastatic breast cancer patients.

背景与研究目的：雌激素受体阳性（ER）/人表皮生长因子受体2阴性（HER2）乳腺癌患者中，内分泌治疗联合CDK4/6抑制剂是首选治疗策略，但不同患者的临床病程仍存在显著异质性。此类重要患者群体仍存在预后或预测生物标志物的未满足临床需求。近期，本团队已证实循环磷脂酰肌醇蛋白聚糖4（glypican-4, GPC4）可作为转移性结直肠癌患者不良预后的新型生物标志物。血浆GPC4水平对乳腺癌患者生存的影响目前尚不明确，本研究就此展开探讨。方法：本研究纳入47例接受CDK4/6抑制剂联合内分泌治疗前的ER阳性/HER2阴性转移性乳腺癌患者。研究终点为24个月总生存期（overall survival, OS）。采用酶联免疫吸附试验检测患者血浆中的GPC4水平。结果：循环GPC4水平升高与高龄、绝经后状态、内脏转移及浸润性小叶癌显著相关。在为期2年的观察随访期内，25.5%的患者死亡。受试者工作特征曲线下面积（receiver operating characteristic curve, ROC-AUC）分析显示，预测OS的AUC为0.713 [95%置信区间：0.555~0.871]；P=0.029，预测OS的GPC4最佳截断值为4.77 ng/mL。随访期内，GPC4水平低于该截断值的患者无一例死亡。Cox回归分析显示，血浆GPC4每增加1个标准差，死亡风险比为2.14 [95%置信区间：1.24~3.67]；P=0.006。结论：综上，本研究表明循环GPC4可作为转移性乳腺癌患者不良生存结局的重要预测因子。