肿瘤突变负荷（TMB）与肿瘤新抗原负荷、T细胞浸润和免疫检查点抑制剂在多种实体瘤类型中的反应相关。根据来自KEYNOTE-158研究的数据，抗PD-1抗体-帕博利珠单抗已被批准用于治疗晚期实体瘤并具有TMB ≥ 10个突变/兆碱基。然而，该试验未包括任何有转移性乳腺癌的患者，因此，关于TMB在乳腺癌免疫检查点抑制剂治疗中作为预测性生物标志物的真正作用，仍有许多问题待解答。在本综述中，我们将讨论在转移性乳腺癌中建立TMB作为免疫治疗受益的预测性生物标志物所面临的挑战和机遇。

Tumor mutational burden (TMB) correlates with tumor neoantigen burden, T cell infiltration, and response to immune checkpoint inhibitors in many solid tumor types. Based on data from the phase II KEYNOTE-158 study, the anti-PD-1 antibody pembrolizumab was granted approval for treating patients with advanced solid tumors and TMB ≥ 10 mutations per megabase. However, this trial did not include any patients with metastatic breast cancer; thus, several questions remain unanswered about the true role of TMB as a predictive biomarker of benefit to immune checkpoint inhibitor therapy in breast cancer. In this review, we will discuss the challenges and opportunities in establishing TMB as a predictive biomarker of benefit to immunotherapy in metastatic breast cancer.