PARP Inhibitors for Breast Cancer Treatment: A Review

Importance

Poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitors have revolutionized the treatment of patients with germline BRCA1/2-associated breast cancer, representing the first targeted therapy capable of improving outcomes in patients with hereditary tumors. However, resistance to PARP inhibitors occurs in almost all patients.

Observations

This narrative review summarizes the biological rationale behind the use of PARP inhibitors in breast cancer, as well as the available evidence, recent progress, and potential future applications of these agents. Recent studies have shown that the benefit of PARP inhibitors extends beyond patients with germline BRCA1/2-associated metastatic breast cancer to patients with somatic BRCA1/2 variants and to those with germline PALB2 alterations. Moreover, these agents proved to be effective both in the metastatic and adjuvant settings. However, patients with metastatic breast cancer usually do not achieve the long-term benefit from PARP inhibitors observed in other tumor types. Mechanisms of resistance have been identified, but how to effectively target them is largely unknown. Ongoing research is investigating both novel therapeutics and new combination strategies to overcome resistance. PARP1-selective inhibitors, by sparing the hematological toxic effects induced by the PARP2 blockade, are promising agents to be combined with chemotherapy, antibody-drug conjugates, and other targeted therapies.

Conclusions and Relevance

Although the efficacy of PARP inhibitors is well established, many questions persist. Future research should focus on identifying predictive biomarkers and therapeutic strategies to overcome resistance. Integrating well-designed translational efforts into all clinical studies is thereby crucial to laying the groundwork for future insights from ongoing research.

Beyond PD(L)-1 Blockade in Microsatellite-Instable Cancers: Current Landscape of Immune Co-Inhibitory Receptor Targeting

High microsatellite instability (MSI-H) derives from genomic hypermutability due to deficient mismatch repair function. Colorectal (CRC) and endometrial cancers (EC) are the tumor types that more often present MSI-H. Anti-PD(L)-1 antibodies have been demonstrated to be agnostically effective in patients with MSI-H cancer, but 50-60% of them do not respond to single-agent treatment, highlighting the necessity of expanding their treatment opportunities. Ipilimumab (anti-CTLA4) is the only immune checkpoint inhibitor (ICI) non-targeting PD(L)-1 that has been approved so far by the FDA for MSI-H cancer, namely, CRC in combination with nivolumab. Anti-TIM3 antibody LY3321367 showed interesting clinical activity in combination with anti-PDL-1 antibody in patients with MSI-H cancer not previously treated with anti-PD(L)-1. In contrast, no clinical evidence is available for anti-LAG3, anti-TIGIT, anti-BTLA, anti-ICOS and anti-IDO1 antibodies in MSI-H cancers, but clinical trials are ongoing. Other immunotherapeutic strategies under study for MSI-H cancers include vaccines, systemic immunomodulators, STING agonists, PKM2 activators, T-cell immunotherapy, LAIR-1 immunosuppression reversal, IL5 superagonists, oncolytic viruses and IL12 partial agonists. In conclusion, several combination therapies of ICIs and novel strategies are emerging and may revolutionize the treatment paradigm of MSI-H patients in the future. A huge effort will be necessary to find reliable immune biomarkers to personalize therapeutical decisions.

The CDK4/6 inhibitors biomarker landscape: The most relevant biomarkers of response or resistance for further research and potential clinical utility

Cyclin-Dependent Kinase 4/6 inhibitors (CDK4/6is) in combination with Endocrine Therapy (ET) represent the standard frontline therapy for patients with Hormone Receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic Breast Cancer (mBC). Clinical activity and efficacy of CDK4/6is-based therapies have been proven both in the endocrine sensitive and resistant settings. Therapy resistance eventually underpins clinical progression to any CDK4/6is-based therapies, yet there is a lack of validated molecular biomarkers predictive of either intrinsic or acquired resistance to CDK4/6is in clinical practice. As the "post-CDK4/6is" landscape for the management of HR-positive/HER2-negative mBC is rapidly evolving with the introduction of novel therapies, there is an urgent need for the definition of clinically relevant molecular biomarkers of intrinsic/acquired resistance mechanisms to CDK4/6is. This narrative review outlines the role of currently approved CDK4/6is-based therapies, describes the most relevant molecular biomarkers of CDK4/6is-resistance, and ultimately provides a perspective on the clinical and research scenario.

Clinicopathological features and survival outcomes of luminal-like breast tumors with estrogen receptor loss at metastatic recurrence: A case-control study

INTRODUCTION

Estrogen receptor (ER) loss at metastatic relapse occurs in up to 20% of luminal-like primary breast tumors. Data about clinicopathological features associated with ER loss and its prognostic significance are limited.

METHODS

In a nested-case-control study, we compared clinicopathological characteristics and clinical outcomes between a cohort of 51 patients with primary ER+ /HER2- and paired triple-negative metastasis (LUM-TN) and two control cohorts of paired early-metastatic ER+ /HER2- (LUM-LUM, n = 50) and triple-negative (TN-TN, n = 49) breast cancers. Stromal tumor-infiltrating lymphocytes (TILs) were assessed according to the TILs Working Group recommendations as continuous and discrete variables with cutoffs (20%, 40%).

RESULTS

LUM-TN tumors had lower ER expression than LUM-LUM tumors, but lower grade and Ki67 than TN-TN cases. Median distant-metastasis free survival was similar for LUM-TN and LUM-LUM cohorts, but significantly longer than in TN-TN cases (log-rank P < 0.001). LUM-TN and TN-TN cohorts had a comparable survival from the time of metastatic recurrence, which was significantly shorter than in patients with LUM-LUM tumors (log-rank P < 0.001). High TILs were associated with worse outcomes in patients with ER loss (P < 0.001).

CONCLUSIONS

Breast tumors with ER loss at metastatic relapse have intermediate features and outcomes compared with metastatic luminal-like and ab initio triple-negative tumors. Further investigation on the biological mechanisms underpinning the loss of ER expression is ongoing.

ESR1 mutations in HR+/HER2-metastatic breast cancer: Enhancing the accuracy of ctDNA testing

Activating mutations of the estrogen receptor alpha gene (ESR1) are common mechanisms of endocrine therapy (ET) resistance in hormone receptor-positive (HR + )/Human Epidermal Growth Factor Receptor 2 (HER2)-negative metastatic breast cancer (MBC). Recent clinical findings emphasize that both old and new generations of selective ER degraders (SERDs) demonstrate enhanced clinical effectiveness in patients with MBC who have detectable ESR1 mutations via liquid biopsy. This stands in contrast to individuals with MBC carrying these mutations and undergoing conventional endocrine monotherapies like aromatase inhibitors (AIs). Liquid biopsy, particularly the analysis of circulating tumor DNA (ctDNA), has emerged as a promising, minimally invasive alternative to conventional tissue-based testing for identifying ESR1 mutations. Within the context of the PADA-1 and EMERALD trials, distinct molecular methodologies and assays, specifically digital droplet PCR (ddPCR) and next-generation sequencing (NGS), have been employed to evaluate the mutational status of ESR1 within ctDNA. This manuscript critically examines the advantages and indications of various ctDNA testing methods on liquid biopsy for HR+/HER2-negative MBC. Specifically, we delve into the capabilities of ddPCR and NGS in identifying ESR1 mutations. Each methodology boasts unique strengths and limitations: ddPCR excels in its analytical sensitivity for pinpointing hotspot mutations, while NGS offers comprehensive coverage of the spectrum of ESR1 mutations. The significance of meticulous sample handling and timely analysis is emphasized, acknowledging the transient nature of cfDNA. Furthermore, we underscore the importance of detecting sub-clonal ESR1 mutations, as these variants can exert a pivotal influence on predicting both endocrine therapy resistance and responsiveness to SERDs. In essence, this work discusses the role of ctDNA analysis for detecting ESR1 mutations and their implications in tailoring effective therapeutic strategies for HR+/HER2- MBC.

Management of patients with HER2-positive metastatic breast cancer after trastuzumab deruxtecan failure

The current treatment of patients with human epidermal growth factor receptor 2 (HER2)-positive advanced breast cancer (ABC) has been greatly impacted in the past decade by the introduction of antibody-drug conjugates (ADCs), which represent a relatively novel therapeutic class with the peculiar ability to deliver otherwise overtly toxic chemotherapeutics to tumor sites by exploiting the specificities of monoclonal antibodies. Indeed, drug engineering refinements in ADC design, such as through the introduction of cleavable linkers and hydrophobic payloads, resulted in improved patient outcomes in recent years. Two different ADCs, namely trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd), have already entered clinical practice for the treatment of HER2-positive ABC. In this scenario, T-DXd has shown to portend better survival outcomes compared to T-DM1, while leaving a large unsought area of unmet medical need upon T-DXd failure. Treatment decision and benefit of cancer drugs following T-DXd still represent an area of clinical controversy, where a preclinical investigation and clinical development should be prioritized. As the pace of innovation is currently accelerating, and with novel ADC formulations advancing in early-phase clinical trials, the whole BC field is changing at an unprecedented rate, with potential broadenings of therapeutic indications. In this review, we present the clinical landscape of HER2-positive advanced BC and discuss our vision on how to tackle T-DXd resistance, providing a perspective on the priority areas of the cancer research in this setting.

Future potential targets of antibody-drug conjugates in breast cancer

Metastatic breast cancer (BC) remains an incurable disease. Besides endocrine and targeted agents, chemotherapy is still a relevant therapeutic option for this disease. Recently, antibody-drug conjugates (ADCs) have shown to overcome the lack of tumor specificity and systemic toxicity typically associated with traditional chemotherapies, thus improving the therapeutic index. To effectively exploit this technological breakthrough, identification of optimal target antigens (Ags) is of utmost importance. To make the ideal target, differential expression of target Ags between healthy and cancer tissues, as well as specific mechanisms of ADC internalization after Ag-antibody interaction are required. Therefore, several in silico strategies to identify and characterize new promising candidate Ags have been developed. If initial in vitro and in vivo positive data are documented, thus providing a biological rationale for further Ag investigation, early phase clinical trials are designed. In BC, these strategies have already led to the development of effective ADCs, namely trastuzumab emtansine (T-DM1), trastuzumab deruxtecan (T-DXd) and sacituzumab govitecan (SG), primarily targeting HER2 and TROP-2. However, promising new Ags are currently under investigation, with encouraging results especially coming from targeting HER3, FRα, Tissue Factor, LIV-1, ROR1-2, and B7-H4. In this review, we describe the landscape of emergent and future potential targets (i.e., other than HER2 and TROP-2) investigated in BC for ADC development. Predominant target expression, function, preclinical rationale, potential clinical implication, as well as preliminary clinical trial results are provided.

Abstract P1-14-05: Pembrolizumab and Oral Metronomic Cyclophosphamide in Patients with Chest Wall Breast Cancer (PERICLES): an immune-biomarker analysis of tumor infiltrating lymphocytes (TILs) and programmed cell death ligand protein 1 (PD-L1)

Background: Breast cancer (BC) with lymphangitic spread to the chest wall is a rare clinical entity affecting about 2% of pts, with poorer survival outcomes. A brisk immune infiltrate is typically reported, with up-regulation of inflammation and immune-tolerogenic genes. PERICLES clinical trial is testing the administration of pembrolizumab 200 mg Q3w plus cyclophosphamide 50 mg daily for BC with chest wall disease. In this exploratory biomarker analysis, we assessed the prevalence of the TILs score and the PD-L1 combined positive score (CPS) obtained from skin biopsies performed at screening.

Methods: PERICLES (NCT03971045) is a single-center, single-arm, interventional phase 2 trial. Main inclusion criteria: histologically confirmed, inoperable, locally recurrent and/or metastatic BC with lymphangitic spread to the chest wall (including and not limited to inflammatory BC); PD-L1 positive (CPS≥1; 22C3 pharmDx®) and/or TILs positive (≥1% of CD3 or CD20-positive cells) disease on skin biopsy obtained at screening; progression to at least one prior cytotoxic treatment; no prior immune checkpoint inhibitors. The primary endpoint is objective response rate as per immune-related RECIST criteria. 46 pts will be required for the study to power for the primary hypothesis. In this analysis, we describe the baseline immune-biomarker status, in the overall population enrolled based on hormone receptor status and HER2. Correlative analyses were provided (significance at p-value&lt; 0.05).

Results: 37 pts were screened with skin biopsy of the chest wall disease (June 2020-June 2022). Biopsy and biomarker analysis were successful in 35 pts. Median age was 58 years (range: 35-79). Among the 35 pts included in the biomarker analysis, 25 (71%) pts had visceral disease and 20 (57%) had skin metastases at the diagnosis of metastatic disease; median number of previous lines of therapies was 4 (range: 1-12) and of chemotherapies was 4 (range: 1-10). 2 (6%) pts had HER2-positive disease, 13 (37%) HR-positive/HER2-negative disease, and 20 (20%) had triple-negative breast cancer (TNBC).

TILs and PD-L1 CPS were &lt; 1 in 15 (43%) pts; 20 pts (57%) were eligible for CPS and/or TILs criteria: 16 (43%) were both PD-L1 positive and TILs positive, 4 only PD-L1 positive. Median PD-L1 CPS score was 5 (range: 0-80%) in the overall population and 17 (range: 2-80%) in eligible patients; 16/35 pts (43%) had CPS≥10. Median TILs score was 0% (range: 0-55%) in the overall population, 0% (range: 0-40%) in the HER2-negative (n=16), 0% (range 0-20%) in the HER2-low (n=18), and 37.5% (range 20-55%) in the HER2-positive (n=2).

No significant differences in baseline characteristics were found between positive and negative biopsies (Table). Considering only the TILs, a statistically significant correlation between HER2-positive status and TILs score was demonstrated (p&lt; 0.001); no other correlations between receptor status (estrogen receptor, progesterone receptor, HER2) and PD-L1 CPS or TILs emerged.

Conclusions: 57% of patients with chest wall BC have skin metastases positive for PD-L1 CPS and/or TILs score ≥1%. To our knowledge, these are the first prospective data on the prevalence of PD-L1 and TILs in metastatic BC with lymphangitic spread to the chest wall, highlighting potential actionability through therapeutic strategies with new immune-oncology agents in this setting.

Table: Characteristics of patients included in the biomarker analysis (n=35) *Calculated with T test or Fisher’s exact test, as appropriate. Keys: BC, breast cancer; CPS, combined positive score; CT, chemotherapy; HR; hormone receptor; n, number; NA; not available; PD-L1, Programmed cell death ligand protein 1; TILs, tumor infiltrating lymphocytes; TNBC, triple negative breast cancer.

Citation Format: Carmine Valenza, Pier Paolo Maria Berton Giachetti, Paola Zagami, Eleonora Nicolò, Dario Trapani, Laura Boldrini, Beatrice Taurelli Salimbeni, Liliana Ascione, Gabriele Antonarelli, Chiara Corti, Angela Esposito, Carmen Criscitiello, Nicola Fusco, Giuseppe Curigliano. Pembrolizumab and Oral Metronomic Cyclophosphamide in Patients with Chest Wall Breast Cancer (PERICLES): an immune-biomarker analysis of tumor infiltrating lymphocytes (TILs) and programmed cell death ligand protein 1 (PD-L1) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-14-05.

Tumor Infiltrating Lymphocytes across Breast Cancer Subtypes: Current Issues for Biomarker Assessment

Tumor-infiltrating lymphocytes (TILs) represent a surrogate biomarker of anti-tumor, lymphocyte-mediated immunity. In early, triple-negative breast cancer, TILs have level 1B of evidence to predict clinical outcomes. TILs represent a promising biomarker to select patients who can experience a better prognosis with de-intensified cancer treatments and derive larger benefits from immune checkpoint inhibitors. However, the assessment and the validation of TILs as a biomarker require a prospective and rigorous demonstration of its clinical validity and utility, provided reproducible analytical performance. With pending data about the prospective validation of TILs' clinical validity to modulate treatments in early breast cancer, this review summarizes the most important current issues and future challenges related to the implementation of TILs assessments across all breast cancer subtypes and their potential integration into clinical practice.

Innovative Therapeutic Approaches for Patients with HER2-Positive Breast Cancer

Overexpression of human epidermal growth factor receptor 2 (HER2), a transmembrane tyrosine kinase receptor, has been described in about 15-20% of breast cancer (BC) and is associated with poor outcomes. Trastuzumab is the first anti-HER2 monoclonal antibody (mAB) that blocks receptor activity but it also activates immune response against cancer cells, thus, revolutionizing the prognosis of patients with HER2-positive BC. Over the years, new therapies have been developed, including other mAbs and tyrosine kinase inhibitors (TKIs) that required multimodal approaches with chemotherapy to optimize their anticancer activity. This chapter gives a comprehensive overview of the last advancements including new approaches and future combinations, which seem to be very promising in overcoming resistance to the traditional anti-HER2 treatments. A modern therapeutic algorithm should include treatment options based on tumour patterns and a patient-centred approach. A proper patient's selection is crucial to derive maximal benefits from a treatment strategy and emerging biomarkers should be integrated along with the HER2 status, which is currently the only validated biomarker in the context of HER2-positive disease. These biomarkers might include molecular features with reported prognostic/predictive significance, such as phosphatidylinositol 3' -kinase (PI3K) or mitogen-activated protein kinase (MAPK) pathways, programmed cell death protein ligand 1 (PD-L1), and tumour-infiltrating lymphocytes (TILs), which all affect prognosis and response to treatments.

The triple negative breast cancer drugs graveyard: a review of failed clinical trials 2017-2022

INTRODUCTION

Triple-negative breast cancer (TNBC) accounts for 15-20% of breast cancers (BC) and has the worst prognosis. It is characterized by the absence of both hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2). TNBC has more limited therapeutic options compared to other subtypes, meaning that there is still a long way to go to discover target treatments.

AREAS COVERED

Our review aims to summarize phase II/III clinical trials enrolling patients with TNBC that have been published between 2017 and 2022 but failed to reach their primary endpoint. We here try to emphasize the limitations and weaknesses noted in negative studies and to point out unexpected results which might be useful to enhance the therapeutic approach to TNBC disease.

EXPERT OPINION

A deeper understanding of the mechanisms behind TNBC heterogeneity allowed to enhance the knowledge of new prognostic and predictive biomarkers of response. However, it is also through several failed clinical trials that we were able to define new therapeutic approaches which improved TNBC patients' clinical outcomes. Nowadays, we still need to overcome several difficulties to fully recognize different intracellular and extracellular pathways that crosstalk in TNBC and the mechanisms of resistance to identify novel tailored-patients' therapies.

PANHER study: a 20-year treatment outcome analysis from a multicentre observational study of HER2-positive advanced breast cancer patients from the real-world setting

Background:

The evolution of therapeutic landscape of human epidermal growth factor receptor-2 (HER2)-positive breast cancer (BC) has led to an unprecedented outcome improvement, even if the optimal sequence strategy is still debated. To address this issue and to provide a picture of the advancement of anti-HER2 treatments, we performed a large, multicenter, retrospective study of HER2-positive BC patients.

Methods:

The observational PANHER study included 1,328 HER2-positive advanced BC patients treated with HER2 blocking agents since June 2000 throughout July 2020. Endpoints of efficacy were progression-free survival (PFS) and overall survival (OS).

Results:

Patients who received a first-line pertuzumab-based regimen showed better PFS (p < 0.0001) and OS (p = 0.004) than those receiving other treatments. Median PFS and mOS from second-line starting were 8 and 28 months, without significant differences among various regimens. Pertuzumab-pretreated patients showed a mPFS and a mOS from second-line starting not significantly affected by type of second line, that is, T-DM1 or lapatinib/capecitabine (p = 0.80 and p = 0.45, respectively). Conversely, pertuzumab-naïve patients receiving second-line T-DM1 showed a significantly higher mPFS compared with that of patients treated with lapatinib/capecitabine (p = 0.004). Median OS from metastatic disease diagnosis was higher in patients treated with trastuzumab-based first line followed by second-line T-DM1 in comparison to pertuzumab-based first-line and second-line T-DM1 (p = 0.003), although these data might be partially influenced by more favorable prognostic characteristics of patients in the pre-pertuzumab era. No significant differences emerged when comparing patients treated with ‘old’ or ‘new’ drugs (p = 0.43), even though differences in the length of the follow-up between the two cohorts should be taken into account.

Conclusion:

Our results confirmed a relevant impact of first-line pertuzumab-based treatment and showed lower efficacy of second-line T-DM1 in trastuzumab/pertuzumab pretreated, as compared with pertuzumab-naïve patients. Our findings may help delineate a more appropriate therapeutic strategy in HER2-positive metastatic BC. Prospective randomized trials addressing this topic are awaited.

Treatment of Capecitabine Corneal Side Effects With Autologous Blood-derived Serum Eye Drops

BACKGROUND/AIM

To describe the clinical progress and management of ocular side effects in a 35-year-old patient with metastatic breast cancer who underwent oral chemotherapy with capecitabine and lapatinib.

MATERIALS AND METHODS

Slit lamp evaluation revealed bilateral perikeratic hyperemia, perilimbal conjunctival edema associated with corneal marginal infiltrates and epithelial and anterior stromal defects in both eyes. Slit lamp examination, in vivo confocal microscopy and anterior-segment optical coherence tomography were highly suggestive for limbal stem cell deficiency. The decision to administer autologous blood- derived serum eye drops was made.

RESULTS

Following administration of autologous blood-derived serum eye drops, corneal marginal infiltrates, epithelial and stromal defects significantly regressed in both eyes after only 10 days. Chemotherapy was resumed and serum eye drops were prescribed simultaneously.

CONCLUSION

Autologous blood-derived serum eye drops may be an adequate therapeutic choice for bilateral corneal lesions detected as ocular side effects of capecitabine.

Statins and immunotherapy: Togetherness makes strength The potential effect of statins on immunotherapy for NSCLC

Background

Recent researches suggested that statins, beside their role in inhibiting endogenous cholesterol synthesis and in cardiovascular prevention, could influence several processes in cancer biology. In fact, a recent meta‐analysis demonstrated that statins could positively influence OS in lung cancer patients.

Aim

There is a lack of large cohort studies that could support a potential antineoplastic role of statins in clinical practice. We collected data from 162 patients treated with immunotherapy for Nonsmall Cell Lung Cancer (NSCLC) in first‐ and second‐line setting to investigate the impact of these drugs on survival parameters.

Methods and Results

In our observational study, we enrolled 162 patients who received immunotherapy for lung cancer between October 2015 and April 2020. We used descriptive statistics to analyze patients' baseline features. Tumor response was evaluated using RECIST version 1.1 guidelines. Uni and multivariate analysis were conducted to investigate the relationship between statin use and response to immunotherapy, using the χ²‐test. We used Kaplan‐Meier curves to estimate OS and PFS in statin and nonstatin users. We included 122 patients in the final analysis. Median PFS was 17.57 months in the statin group and 9.57 months in the nonstatin group, with a P = <.001. Moreover, median OS was superior in the statin‐users group, with a statistically significant difference (19.94 vs 10.94 months, P = <.001).

Conclusion

Although in our study, statin use positively correlates with PFS and OS in lung cancer patient treated with immunotherapy, these results require a further validation with randomized clinical trials.