Longitudinal profiling identifies co-occurring BRCA1/2 reversions, TP53BP1, RIF1 and PAXIP1 mutations in PARP inhibitor-resistant advanced breast cancer

BACKGROUND

Resistance to therapies that target homologous recombination deficiency (HRD) in breast cancer limits their overall effectiveness. Multiple, preclinically validated, mechanisms of resistance have been proposed, but their existence and relative frequency in clinical disease are unclear, as is how to target resistance.

PATIENTS AND METHODS

Longitudinal mutation and methylation profiling of circulating tumour (ct)DNA was carried out in 47 patients with metastatic BRCA1-, BRCA2- or PALB2-mutant breast cancer treated with HRD-targeted therapy who developed progressive disease-18 patients had primary resistance and 29 exhibited response followed by resistance. ctDNA isolated at multiple time points in the patient treatment course (before, on-treatment and at progression) was sequenced using a novel >750-gene intron/exon targeted sequencing panel. Where available, matched tumour biopsies were whole exome and RNA sequenced and also used to assess nuclear RAD51.

RESULTS

BRCA1/2 reversion mutations were present in 60% of patients and were the most prevalent form of resistance. In 10 cases, reversions were detected in ctDNA before clinical progression. Two new reversion-based mechanisms were identified: (i) intragenic BRCA1/2 deletions with intronic breakpoints; and (ii) intragenic BRCA1/2 secondary mutations that formed novel splice acceptor sites, the latter being confirmed by in vitro minigene reporter assays. When seen before commencing subsequent treatment, reversions were associated with significantly shorter time to progression. Tumours with reversions retained HRD mutational signatures but had functional homologous recombination based on RAD51 status. Although less frequent than reversions, nonreversion mechanisms [loss-of-function (LoF) mutations in TP53BP1, RIF1 or PAXIP1] were evident in patients with acquired resistance and occasionally coexisted with reversions, challenging the notion that singular resistance mechanisms emerge in each patient.

CONCLUSIONS

These observations map the prevalence of candidate drivers of resistance across time in a clinical setting, information with implications for clinical management and trial design in HRD breast cancers.

Abstract ES6-4: Parp inhibitors for brca1/2mutation associated breast cancer

More than 15 years ago we and others showed the use of potent PARP1 inhibitors (PARPi), that both inhibit the catalytic activity of the PARP1 enzyme and trap PARP1 onto DNA, generate a “synthetic lethal” interaction with the malignant cell specific loss of function of genes crucial for homologous recombination (HR) gene function. This phenomenon has now been exploited with therapeutic intent in several contexts leading to approved single agent PARPi treatments for advanced forms of ovarian, prostate, pancreatic and breast cancers. These approvals have in large part been associated a biomarker requirement for evidence of loss of function of HR. Recently a number of trials have investigated PARPi in a (neo)adjuvant breast cancer treatment (NACT) setting in patients with (or enriched for) HR deficiency. These have included phase II neoadjuvant PARPi studies such as the NeoTALA study using single agent talazoparib in germline BRCA1 and BRCA2 mutation carriers and the combination chemotherapy and olaparib therapy studies GeparOLA and PARTNER, enriched for HR deficient breast cancer, that have reported important signals with regard efficacy and tolerability. Two recent phase III trials have influenced recent early breast cancer treatment guidelines. These are the BrighTNess trial in the neoadjuvant setting and OlympiA in the post-(neo)adjuvant setting. BrighTNess recruited patients with biologically heterogeneous triple negative breast cancer (TNBC) and used the weak PARP1 trapping PARPi veliparib and OlympiA restricted eligibility to patients with the germline “pathogenic” or “likely pathogenic” mutation in BRCA1 or BRCA2 but included patients with hormone receptor positive breast cancer. BrighTNess did not show convincing evidence of benefit to the addition of veliparib to standard of care in TNBC NACT but has shown the benefit to the addition of carboplatin to sequential paclitaxel-AC NACT with significant improvements in event free survival (HR 0.57 ) compared to sequential paclitaxel-AC alone. OlympiA has reported following an interim analysis showing 12 months of olaparib in the post-(neo)adjuvant chemotherapy setting improves both invasive disease free and distant disease free survival by approximately 40% with highly statistically significant hazard ratios of 0.58 and 0.57 respectively that met pre-specified early stopping boundaries. The publication of results for OlympiA has led to rapid updates of both genetic testing and treatment international guidelines for BRCA1 and BRCA2 mutation associated breast cancer to include use of olaparib in patients meeting the eligibility criteria for the trial. The lecture will both explore the data and the implications for practice of the adoption of these guidelines and some of the ongoing questions to be addressed by ongoing clinical trial and translational research initiatives.

Citation Format: ANJ Tutt. Parp inhibitors for brca1/2mutation associated breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr ES6-4.

Triple negative tumours: a critical review

Breast cancer is a heterogeneous disease that encompasses several distinct entities with remarkably different biological characteristics and clinical behaviour. Currently, breast cancer patients are managed according to algorithms based on a constellation of clinical and histopathological parameters in conjunction with assessment of hormone receptor (oestrogen and progesterone receptor) status and HER2 overexpression/gene amplification. Although effective tailored therapies have been developed for patients with hormone receptor-positive or HER2+ disease, chemotherapy is the only modality of systemic therapy for patients with breast cancers lacking the expression of these markers (triple-negative cancers). Recent microarray expression profiling analyses have demonstrated that breast cancers can be systematically characterized into biologically and clinically meaningful groups. These studies have led to the re-discovery of basal-like breast cancers, which preferentially show a triple-negative phenotype. Both triple-negative and basal-like cancers preferentially affect young and African-American women, are of high histological grade and have more aggressive clinical behaviour. Furthermore, a significant overlap between the biological and clinical characteristics of sporadic triple-negative and basal-like cancers and breast carcinomas arising in BRCA1 mutation carriers has been repeatedly demonstrated. In this review, we critically address the characteristics of basal-like and triple-negative cancers, their similarities and differences, their response to chemotherapy as well as strategies for the development of novel therapeutic targets for these aggressive types of breast cancer. In addition, the possible mechanisms are discussed leading to BRCA1 pathway dysfunction in sporadic triple-negative and basal-like cancers and animal models for these tumour types.

Exploiting the DNA repair defect in BRCA mutant cells in the design of new therapeutic strategies for cancer

Individuals harboring germ-line mutations in the BRCA1 or BRCA2 genes are at highly elevated risk of a variety of cancers. Ten years of research has revealed roles for BRCA1 and BRCA2 in a wide variety of cellular processes. However, it seems likely that the function of these proteins in DNA repair is critically important in maintaining genome stability. Despite this increasing knowledge of the defects present in BRCA-deficient cells, BRCA mutation carriers developing cancer are still treated similarly to sporadic cases. Here we describe our efforts, based on understanding the DNA repair defects in BRCAdeficient cells, to define the optimal existing treatment for cancers arising in BRCA mutation carriers and, additionally, the development of novel therapeutic approaches. Finally, we discuss how therapies developed to treat BRCA mutant tumors might be applied to some sporadic cancers sharing similar specific defects in DNA repair.

The role of positron emission tomography in the management of colorectal cancer

Positron emission tomography (PET) is a functional imaging modality that has made the transition from the research environment to the clinical environment over the last 10 years. Its major role is in the field of oncology where it is being used increasingly in the management of several tumour types including colorectal cancer. This review aims to outline the current and future role of PET scanning in the field of colorectal cancer.

Palliative chemotherapy in recurrent carcinoma of the cervix: an audit of the use of ifosfamide and review of the literature

A review was conducted on 34 patients treated with intravenous ifosfamide for relapsed, inoperable carcinoma of the cervix between 1988 and 1996. The median age of patients was 44 years. Thirty-two patients had squamous cell carcinoma and 2 had adenocarcinoma. Radiotherapy had been used in primary management in 33, neo-adjuvant platinum chemotherapy in 7, and previous palliative chemotherapy in 11. Symptomatic response was assessed with respect to the symptom requiring palliaton. 25 patients failed to complete 6 cycles of chemotherapy: due to progressive disease in 14, lack of symptom response in 2, and toxicity in 11 of whom 7 had encephalopathy sufficient to abandon treatment. 32 patients were evaluable for objective response. Pathologic complete response (CR) was achieved in 1 patient, and partial response (PR) was achieved in 3 patients. The objective response rate was 11.8%. Symptomatic response throughout treatment occurred in 8 patients (24%); objective response was seen in only 3 (1 CR, 2 PR) of them and progressive disease in the remaining 5. Response duration in the 4 objective responders was 25 months in the patient with CR and 4, 6 and 8 weeks in the 3 patients with PR. In conclusion, ifosfamide, as given, is associated with unacceptable toxicity and insufficient symptomatic efficacy for use as a palliative treatment in patients with relapsed carcinoma of the cervix.