The success of cancer immunotherapy with immune checkpoint blockade (ICB) has demonstrated the importance of targeting a preexisting immune response in a broad spectrum of tumors. This is particularly novel and relevant for less immunogenic tumors, such as breast cancer (BC), where the efficacy of ICB was more evident in the triple-negative (TNBC) subtype, in earlier stages, and in association with chemotherapy. Tumors harboring homologous recombination DNA repair (HRR) deficiency (HRD) are supposed to have a higher number of mutations, hence a higher tumor mutational burden, which could potentially make them more sensitive to immunotherapy. However, the mechanisms involved in ICB sensitivity and patient selection are still yet to be defined in BC: whether the innate system could play a role and how the adaptive immunity could be linked with HRR pathways are the two key points of debate that we will discuss in this article. The aim of this review was to close the loop between what was found in clinical trial results so far, go back to laboratory theory and preclinical results and point out what needs to be clarified from now on.

免疫检查点阻断（ICB）癌症免疫疗法的成功证明了针对广泛肿瘤中预先存在的免疫反应的重要性。这对于免疫原性较低的肿瘤（例如乳腺癌（BC））来说尤其新颖且相关，在乳腺癌（BC）等早期阶段，ICB 的疗效在三阴性（TNBC）亚型中更为明显，并且与化疗相关。具有同源重组 DNA 修复 (HRR) 缺陷 (HRD) 的肿瘤被认为具有更高数量的突变，因此肿瘤突变负担更高，这可能使它们对免疫治疗更加敏感。然而，BC 中涉及 ICB 敏感性和患者选择的机制仍有待确定：先天系统是否可以发挥作用以及适应性免疫如何与 HRR 通路联系起来是我们将讨论的两个关键争论点在本文中。本次综述的目的是闭合迄今为止临床试验结果之间的循环，回到实验室理论和临床前结果，并指出从现在开始需要澄清的内容。