【原】基因突变晚期乳腺癌患者耐药逆转机制

　　对于乳腺癌易感基因（BRCA）突变的晚期乳腺癌患者，多腺苷二磷酸核糖聚合酶（PARP）抑制剂（例如奥拉帕利、他拉唑帕利）和铂类化疗等DNA破坏疗法的耐药机制尚不明确。对这些临床耐药人群进行研究，有助于预防或克服治疗失败。

　　2020年2月20日，欧洲肿瘤内科学会《肿瘤学报》在线发表美国哈佛大学、达纳法伯癌症研究所、布莱根医院和波士顿妇女医院、麻省理工学院布罗德研究所、麻省总医院、国家癌症研究所、希望之城国家医学中心、耶鲁大学、麻省大学的研究报告，探讨了BRCA突变晚期乳腺癌患者PARP抑制剂或铂类化疗耐药的基因逆转和非逆转机制。

　　该研究从8例PARP抑制剂（奥利帕利）或铂类化疗耐药前后的BRCA突变晚期乳腺癌患者获取肿瘤活检标本，对各个肿瘤、生殖细胞DNA、循环肿瘤DNA进行全外显子组测序，对肿瘤进行RNA测序，并对肿瘤切片进行RAD51免疫组织化学染色，以评估完整同源重组功能。

　　结果，其中BRCA1、BRCA2突变各4例，PARP抑制剂治疗、铂类化疗各4例。

　　上述DNA破坏疗法耐药后，4例患者（50%）发生至少一种体细胞基因逆转变化，可能引起肿瘤DNA或循环肿瘤DNA测序检出有功能的BRCA蛋白。

　　2例生殖细胞BRCA1突变患者发生基因组变化，可以通过增加DNA末端切除恢复同源重组，其中TP53BP1缺失1例、MRE11A扩增1例。

　　所有基因组逆转患者耐药后均发生RAD51突变，与同源重组重建一致。

　　所有耐药后RAD51突变患者都对后续DNA破坏疗法产生原发耐药。

　　因此，该研究结果表明，BRCA基因组逆转是最常见的耐药机制，发生于半数患者。2例患者发现引起DNA末端切除增加的新序列变化，并且对其进行靶向治疗可能获益。免疫组织化学染色表明，RAD51突变与基因组数据的BRCA蛋白质功能状态一致，并可预测对后续DNA破坏疗法的效果，支持RAD51突变可以作为有临床意义的生物标志，值得进一步探索。

Ann Oncol. 2020 Feb 20. [Epub ahead of print]

Reversion and non-reversion mechanisms of resistance to PARP inhibitor or platinum chemotherapy in BRCA1/2-mutant metastatic breast cancer.

Adrienne G. Waks, Ofir Cohen, Bose Kochupurakkal, Dewey Kim, Connor E. Dunn, Jorge Buendia Buendia, Seth Wander, Karla Helvie, Maxwell R. Lloyd, Lori Marini, Melissa E. Hughes, Samuel S. Freeman, S. Percy Ivy, Joseph Geradts, Steve Isakoff, Patricia LoRusso, Viktor A. Adalsteinsson, Sara M. Tolaney, Ursula Matulonis, Ian E. Krop, Alan D. D'Andrea, Eric P. Winer, Nancy U. Lin, Geoffrey I. Shapiro, Nikhil Wagle.

Dana-Farber Cancer Institute, Boston, MA; Brigham and Women's Hospital, Boston, MA; Broad Institute of MIT and Harvard, Cambridge, MA; Harvard Medical School, Boston, MA; Massachusetts General Hospital, Boston, MA; National Cancer Institute, Bethesda, MD; City of Hope Comprehensive Cancer Center, Duarte, CA; Yale Cancer Center, New Haven, CT; University of Massachusetts Medical School, Worcester, MA.

HIGHLIGHTS

• We analyzed mechanisms of resistance to PARP inhibitor/platinum chemotherapy in BRCA1/2-mutant metastatic breast cancer.

• Genomic reversion to functional BRCA1/2 protein was identified in one-half of patients.

• Upregulation of DNA end resection was identified as a resistance mechanism in two additional patients.

• RAD51 foci assessed by immunohistochemistry correlated with clinical response to PARP inhibitor/platinum.

• RAD51 focus staining warrants further exploration as a biomarker for clinical use.

BACKGROUND: Little is known about mechanisms of resistance to PARP inhibitors and platinum chemotherapy in patients with metastatic breast cancer and BRCA1/2 mutations. Further investigation of resistance in clinical cohorts may point to strategies to prevent or overcome treatment failure.

PATIENTS AND METHODS: We obtained tumor biopsies from metastatic breast cancer patients with BRCA1/2 deficiency before and after acquired resistance to PARP inhibitor or platinum chemotherapy. Whole exome sequencing was performed on each tumor, germline DNA, and circulating tumor DNA. Tumors underwent RNA sequencing, and immunohistochemical staining for RAD51 foci on tumor sections was performed for functional assessment of intact homologous recombination.

RESULTS: Pre- and post-resistance tumor samples were sequenced from 8 patients (4 with BRCA1 and 4 with BRCA2 mutation; 4 treated with PARP inhibitor and 4 with platinum). Following disease progression on DNA-damaging therapy, four patients (50%) acquired at least one somatic reversion alteration likely to result in functional BRCA1/2 protein detected by tumor or circulating tumor DNA sequencing. Two patients with germline BRCA1 deficiency acquired genomic alterations anticipated to restore homologous recombination through increased DNA end resection: loss of TP53BP1 in one patient and amplification of MRE11A in another. RAD51 foci were acquired post-resistance in all patients with genomic reversion, consistent with reconstitution of homologous recombination. All patients whose tumors demonstrated RAD51 foci post-resistance were intrinsically resistant to subsequent lines of DNA-damaging therapy.

CONCLUSIONS: Genomic reversion in BRCA1/2 was the most commonly observed mechanism of resistance, occurring in 4 of 8 patients. Novel sequence alterations leading to increased DNA end resection were seen in two patients, and may be targetable for therapeutic benefit. The presence of RAD51 foci by immunohistochemistry was consistent with BRCA1/2 protein functional status from genomic data and predicted response to later DNA-damaging therapy, supporting RAD51 focus formation as a clinically useful biomarker.

KEYWORDS: BRCA1, BRCA2, breast cancer, PARP inhibitor, platinum

DOI: 10.1016/j.annonc.2020.02.008