PolyADP-ribose polymerase (PARP) inhibitors (PARPis) represent the first clinically approved drugs able to provoke “synthetic lethality” in patients with homologous recombination-deficient (HRD) tumors. Four PARPis have just received approval for the treatment of several types of cancer. Besides, another three additional PARPis underlying the same mechanism of action are currently under investigation. Despite the success of these targeted agents, the increasing use of PARPis in clinical practice for the treatment of different tumors raised the issue of PARPis resistance, and the consequent disease relapse and dismal prognosis for patients. Several mechanisms of resistance have been investigated, and ongoing studies are currently focusing on strategies to address this challenge and overcome PARPis resistance. This review aims to analyze the mechanisms underlying PARPis resistance known today and discuss potential therapeutic strategies to overcome these processes of resistance in the future.

Ovarian cancer treatment strategy is mainly based on three pillars: cytoreductive surgery, platinum-based chemotherapy, and targeted therapies. The latter in the last decade has provided a remarkable improvement in progression free patients and, hopefully, in overall survival. In particular, poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitors exploit BRCA 1/2 mutations and DNA damage response deficiencies, which are believed to concern up to 50% of high grade epithelial ovarian cancer cases. While these agents have an established role in ovarian cancer treatment strategy in BRCA mutated and homologous recombination deficient patients, an appropriate predictive molecular test to select patients is lacking in clinical practice. At the same time, the impressive results of immunotherapy in other malignancies, have opened the space for the introduction of immune-stimulatory drugs in ovarian cancer. Despite immune checkpoint inhibitors as a monotherapy bringing only modest efficacy when assessed in pretreated ovarian cancer patients, the combination with chemotherapy, anti-angiogenetics, PARP inhibitors, and radiotherapy is believed to warrant further investigation. We reviewed literature evidence on PARP inhibitors and immunotherapy in ovarian cancer treatment.

The worldwide approval of the combination maintenance therapy of olaparib and bevacizumab in advanced high-grade serous ovarian cancer requires complex molecular diagnostic assays that are sufficiently robust for the routine detection of driver mutations in homologous recombination repair (HRR) genes and genomic instability (GI), employing formalin-fixed (FFPE) paraffin-embedded tumor samples without matched normal tissue. We therefore established a DNA-based hybrid capture NGS assay and an associated bioinformatic pipeline that fulfils our institution’s specific needs. The assay´s target regions cover the full exonic territory of relevant cancer-related genes and HRR genes and more than 20,000 evenly distributed single nucleotide polymorphism (SNP) loci to allow for the detection of genome-wide allele specific copy number alterations (CNA). To determine GI status, we implemented an %CNA score that is robust across a broad range of tumor cell content (25–85%) often found in routine FFPE samples. The assay was established using high-grade serous ovarian cancer samples for which BRCA1 and BRCA2 mutation status as well as Myriad MyChoice homologous repair deficiency (HRD) status was known. The NOGGO (Northeastern German Society for Gynecologic Oncology) GIS (GI-Score) v1 assay was clinically validated on more than 400 samples of the ENGOT PAOLA-1 clinical trial as part of the European Network for Gynaecological Oncological Trial groups (ENGOT) HRD European Initiative. The “NOGGO GIS v1 assay” performed using highly robust hazard ratios for progression-free survival (PFS) and overall survival (OS), as well a significantly lower dropout rate than the Myriad MyChoice clinical trial assay supporting the clinical utility of the assay. We also provide proof of a modular and scalable routine diagnostic method, that can be flexibly adapted and adjusted to meet future clinical needs, emerging biomarkers, and further tumor entities.

Tumor Treating Fields (TTFields) are electric fields that disrupt processes critical for cancer cell viability and tumor progression. The pivotal, phase 3 ENGOT-ov50/GOG-3029/INNOVATE-3 study evaluated efficacy and safety of TTFields therapy with paclitaxel (PTX) vs PTX in patients with platinum-resistant ovarian cancer (PROC). Adult patients with PROC with ≤ 5 total prior lines of therapy (LOT), including ≤ 2 prior LOT for platinum-resistant disease, and ECOG PS of 0-1 were randomized 1:1 to receive TTFields (200 kHz; ≥ 18 h/day) + PTX (80 mg/m² weekly) or PTX. Primary endpoint was overall survival (OS). Exploratory post-hoc analyses assessed OS in pegylated liposomal doxorubicin (PLD)-naive patients. Between March 2019 and November 2021, 558 patients (ECOG PS 0, 60.2 %; median [range] age, 62 [22-91] years) were assigned TTFields+PTX (n = 280) or PTX (n = 278). 24.4 % had 4 + prior LOT. Median OS was 12.2 months with TTFields+PTX vs 11.9 months with PTX (HR, 1.01; 95 % CI, 0.83-1.24; p = 0.89). Grade ≥ 3 adverse events (AEs) were similar between treatment groups. Grade 1/2 device-related skin AEs occurred in 83.6 % of patients receiving TTFields therapy. In exploratory post-hoc analysis in PLD-naive patients, median OS was 16 months with TTFields+PTX (n = 113) vs 11.7 months with PTX (n = 88; nominal HR, 0.67; 95 % CI, 0.49-0.94; p = 0.03). No new safety signals were identified. TTFields+PTX did not significantly improve OS compared with PTX in the intent-to-treat population. An exploratory post-hoc analysis suggests a potentially favorable benefit-risk profile for TTFields therapy in PLD-naive patients.

Cervical cancer is the fourth most common type of cancer in women worldwide. It is associated with a high death rate, despite the fact that it is a nearly 100% preventable disease because of very effective primary and secondary preventive strategies. Advanced and recurrent disease is uncurable with a high relapse risk and the second-line therapies are limited with modest response rates and short durability. Investigating alternative mechanisms of action is crucial because of the high request for effective new therapies. Tisotumab vedotin (TV) is the first antibody-drug conjugated to target a cell surface-expressed tissue factor, and preliminary data in patients with metastatic and recurrent cervical cancer have been promising. In addition, the trials showed a favorable tolerability profile, with limited incidence of grade 3 or worse adverse events. According to the data of ENGOT-cx6/GOG-3023/innovaTV 204, the US Food and Drug Administration granted expedited approval of TV on September 20, 2021, for women with recurrent or metastatic cervical cancer. Actually, two other trials testing TV alone or in combination with other agents are ongoing. ENGOT-cx8/GOG-3024/innovaTV 205 is a Phase Ib/II trial of TV in combination with platinum or bevacizumab or pembrolizumab, in patients with recurrent or metastatic cervical cancer who have not received prior systemic therapy or who have progressed after no more than two prior systemic therapies. ENGOT-cx12/GOG-3057/InnovaTV 301 is a Phase 3 trial of TV vs investigator’s choice chemotherapy in patients with advanced or recurrent cervical cancer who had received no more than 2 prior chemotherapy lines. The outcomes of these two trials will potentially confirm and reinforce the use of TV as a new standard of care in advanced or recurrent cervical cancer.