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.

Phase II study of ceralasertib (AZD6738) in combination with durvalumab in patients with advanced/metastatic melanoma who have failed prior anti-PD-1 therapy

BACKGROUND

Modulating the DNA damage response and repair (DDR) pathways is a promising strategy for boosting cancer immunotherapy. Ceralasertib (AZD6738) is an oral inhibitor of the serine/threonine protein kinase ataxia telangiectasia and Rad3-related protein, which is crucial for DDR.

PATIENTS AND METHODS

This phase II trial evaluated ceralasertib plus durvalumab for the treatment of patients with metastatic melanoma who had failed anti-programmed cell death protein 1 therapy.

RESULTS

Among the 30 patients, we observed an overall response rate of 31.0% and a disease control rate of 63.3%. Responses were evident across patients with acral, mucosal, and cutaneous melanoma. The median duration of response was 8.8 months (range, 3.8-11.7 months). The median progression-free survival was 7.1 months (95% confidence interval, 3.6-10.6 months), and the median overall survival was 14.2 months (95% confidence interval, 9.3-19.1 months). Common adverse events were largely hematologic and manageable with dose interruptions and reductions. Exploratory biomarker analysis suggested that tumors with an immune-enriched microenvironment or alterations in the DDR pathway were more likely to respond to the study treatment.

CONCLUSION

We conclude that ceralasertib in combination with durvalumab has promising antitumor activity among patients with metastatic melanoma who have failed anti-programmed cell death protein 1 therapy, and constitute a population with unmet needs.