BRCA1/2突变三阴性乳腺癌对蒽环类药物耐药机制研究

Triple-negative breast cancer (TNBC) is defined as tumors that lack expression of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). TNBC exhibits an aggressive phenotype and is strongly associated with BRCA1/2-related breast cancer. The BRCA1/2 mutation is a potential drug target in TNBC. BRCA1 and BRCA2 encode proteins that are crucial for the accurate repair of DNA double-strand breaks (DSBs) by homologous recombination (HR). Although the related therapy approach has shown considerable promise, drug resistance has become a significant issue. Recent data have revealed multiple mechanisms for resistance to PARP inhibitors and platinum. However, there has been no report on the mechanisms of resistance to anthracycline until now. In our previous study, we carried out a clinical translational study in 956 TNBC patients. We investigated the association between BRCA1 mutation carriers and response to neoadjuvant anthracycline-based therapy in Chinese women with BRCA1/2-mutated TNBC. We found that BRCA1 mutation carriers were more sensitive to anthracycline-based neoadjuvant regimens than non-carriers, resulting in a very high pCR (pathologic complete response) rate (pCR rate, 57.1% versus 29.0%). Patients with pCR may derive survival benefits compared with non-pCR patients. In spite of this, not all BRCA1-mutated TNBCs respond equally well to this type of therapy. There are still nearly half of all BRCA1-mutated TNBC patients who do not achieve pCR. In this study, we will investigate the mechanisms of resistance in BRCA1/2-mutated TNBC patients with poor responses to neoadjuvant anthracycline-based therapy. We will extend our sample size, including blood samples, fresh core needle biopsy tumor tissues before treatment, and fresh tumor tissues procured after surgery. We will explore the partial activity of BRCA1/2-mutated alleles and the BRCA1/2 secondary mutation. We will also investigate the additional alterations in HR pathways involved in anthracycline resistance. Finally, we will identify whether P-glycoprotein (Pgp)-mediated resistance exists. Our goal is to explain the mechanisms of chemoresistance to anthracycline in BRCA1/2-mutated TNBC patients and thus enable the design of approaches that either avoids, delays, or reverses drug resistance. The results may further guide clinical treatment of BRCA1/2-mutated TNBC patients.

BRCA1/2基因突变是三阴性乳腺癌治疗的新靶点，但肿瘤耐药是BRCA1/2突变乳腺癌临床研究面临的挑战。目前研究多集中在BRCA1/2突变肿瘤对铂类和PARP1抑制剂的耐药机制上，而BRCA1/2突变乳腺癌对蒽环类药物的耐药机制国内外迄今未见报道。在本课题的前期工作中，我们发现在接受蒽环新辅助化疗的患者中，BRCA1突变患者较非突变患者有更高的病理完全缓解率，达到病理完全缓解的患者具有更长的生存获益；尽管如此，仍有近半数的BRCA1突变三阴性乳腺癌未获得病理完全缓解。本课题以接受蒽环术前化疗但未达到病理完全缓解的BRCA1/2突变三阴性乳腺癌为研究对象，拟从BRCA1/2基因自身、同源重组通路其他因素及药物代谢三个方面，利用外周血、术前穿刺和术后肿瘤组织样本，探讨BRCA1/2突变三阴性乳腺癌对蒽环类药物的耐药机制。本研究将对BRCA1/2突变三阴性乳腺癌的个体化治疗提供新的思路和策略。

BRCA1/2基因突变是三阴性乳腺癌治疗的新靶点，但肿瘤耐药是BRCA1/2突变乳腺癌临床研究面临的挑战。目前研究多集中在BRCA1/2突变肿瘤对铂类和PARP1抑制剂的耐药机制上，而BRCA1/2突变乳腺癌对蒽环类药物的耐药机制国内外迄今未见报道。本课题以接受蒽环术前化疗但未达到病理完全缓解的BRCA1/2突变三阴性乳腺癌为研究对象，从BRCA1/2基因自身、同源重组通路其他因素及药物代谢三个方面，利用外周血、术前穿刺和术后肿瘤组织样本，探讨BRCA1/2突变三阴性乳腺癌对蒽环类药物的耐药机制。（1）我们共筛选出101例携带致病BRCA1/2胚系突变或胚系重排乳腺癌样本（34例携带BRCA1胚系致病突变，67例携带BRCA2胚系致病突变），分析外周血中和肿瘤组织中的BRCA1/2突变，研究结果显示101名外周血检测到致病的BRCA1/2胚系突变或重排在组织样本中均检测到和外周血相同位置的BRCA1/2突变。进一步在4例（4/34，11.8%）BRCA1携带者的肿瘤组织中检测到BRCA1的二次突变；14例（14/67，20.9%）BRCA2携带者的肿瘤组织中检测到BRCA2的二次突变。（2）采用基因panel测序结合Sanger测序验证的方法检测并对比外周血、术前穿刺样本和术后肿瘤组织检中同源重组通路其它基因突变状态。我们发现BRCA2突变患者同时携带同源重组基因RAD50基因突变，进一步我们对7657例患者的外周血DNA基因组进行RAD50基因突变检测，结果显示携带RAD50基因胚系突变患者的RFS，DRFS和DSS明显差于非突变携带者。多因素分析证实携带RAD50基因胚系突变是独立于诊断年龄、肿瘤大小、肿瘤等级、淋巴结状态、ER状态、PR状态、HER2状态和辅助治疗情况的独立预测因素（RFS，adjusted HR：2.66，95% CI：1.18-5.98，P=0.018；DSS，adjusted HR：4.36，95% CI：1.58-12.03，P=0.004）。（3）我们还对同源重组通路中感受DNA双链断裂损伤并引起诸多DNA损伤信号反应通路的主开关分子ATM基因进行了研究，我们发现携带ATM基因胚系突变的乳腺癌患者更易更易出现淋巴结转移。本研究将对BRCA1/2突变三阴性乳腺癌的个体化治疗提供新的思路和策略。