Cyclin-Dependent Kinase 4/6 Inhibitor Outcomes in Patients With Advanced Breast Cancer Carrying Germline Pathogenic Variants in DNA Repair-Related Genes

Tailoring neo/adjuvant systemic therapy in breast cancer: "The advent of a personalized approach"-The Breast-Gynecological and Immuno-Oncology International Cancer Conference (BGICC) consensus and recommendations

BACKGROUND

The management of early breast cancer (BC) has witnessed an uprise in the use of neoadjuvant therapy and a remarkable reshaping of the systemic therapy postneoadjuvant treatment in the last few years, with the evolution of many controversial clinical situations that require consensus.

METHODS

During the 14th Breast-Gynecological and Immuno-Oncology International Cancer Conference held in Egypt in 2022, a panel of 44 BC experts from 13 countries voted on statements concerning debatable challenges in the neo/adjuvant treatment setting. The recommendations were subsequently updated based on the most recent data emerging. A modified Delphi approach was used to develop this consensus. A consensus was achieved when ≥75% of voters selected an answer.

RESULTS AND CONCLUSIONS

The consensus recommendations addressed different escalation and de-escalation strategies in the setting of neoadjuvant therapy for early BC. The recommendations recapitulate the available clinical evidence and expert opinion to individualize patient management and optimize therapy outcomes. Consensus was reached in 63% of the statements (52/83), and the rationale behind each statement was clarified.

Novel Treatment Strategies for Hormone Receptor (HR)-Positive, HER2-Negative Metastatic Breast Cancer

Estrogen receptor (ER)-positive breast cancer (BC) is the most common BC subtype. Endocrine therapy (ET) targeting ER signaling still remains the mainstay treatment option for hormone receptor (HR)-positive BC either in the early or in advanced setting, including different strategies, such as the suppression of estrogen production or directly blocking the ER pathway through SERMs-selective estrogen receptor modulators-or SERDs-selective estrogen receptor degraders. Nevertheless, the development of de novo or acquired endocrine resistance still remains challenging for oncologists. The use of novel ET combined with targeted drugs, such as cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, has significantly improved long-term outcome rates, thus changing the therapeutic algorithm for metastatic BC (MBC) and recently the therapeutic strategy in the adjuvant setting for early high-risk BC. Eluding the resistance to CDK4/6 inhibitors combined with ET is currently an unmet medical need, and there is disagreement concerning the best course of action for patients who continue to progress after this combination approach. Genetic changes in the tumor along its growth uncovered by genomic profiling of recurrent and/or metastatic lesions through tumor and/or liquid biopsies may predict the response or resistance to specific agents, suggesting the best therapeutic strategy for each patient by targeting the altered ER-dependent pathway (novel oral SERDs and a new generation of anti-estrogen agents) or alternative ER-independent signaling pathways such as PI3K/AKT/mTOR or tyrosine kinase receptors (HER2 mutations or HER2 low status) or by inhibiting pathways weakened through germline BRCA1/2 mutations. These agents are being investigated as single molecules and in combination with other target therapies, offering promising weapons to overcome or avoid treatment failure and propose increasingly more personalized treatment approaches. This review presents novel insights into ET and other targeted therapies for managing metastatic HR+/HER2- BC by exploring potential strategies based on clinical evidence and genomic profiling following the failure of the CDK4/6i and ET combination.

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.

Cost-Effectiveness Analysis of Adjuvant Olaparib Versus Watch and Wait in the Treatment of Germline BRCA1/2-Mutated, High-Risk, HER2-Negative Early Breast Cancer in Sweden

INTRODUCTION

This study evaluated the cost effectiveness of adjuvant olaparib versus watch and wait (WaW) in patients with germline breast cancer susceptibility gene 1/2 (gBRCA1/2)-mutated, high-risk, human epidermal growth factor receptor 2 (HER2)-negative early breast cancer (eBC), previously treated with neoadjuvant or adjuvant chemotherapy, from a Swedish healthcare perspective.

METHODS

A five-state (invasive disease-free survival [IDFS], non-metastatic breast cancer [non-mBC], early-onset mBC, late-onset mBC, death) semi-Markov state transition model with a lifetime horizon was developed. Transition probabilities were informed by data from the Phase III OlympiA trial, supplemented with data from additional studies in BRCA-mutated, HER2-negative mBC. Health state utilities were derived via mapping of OlympiA data and supplemented by literature estimates. Treatment, adverse events and other medical costs were extracted from publicly available Swedish sources. Incremental cost per life-year (LY) and quality-adjusted life-year (QALY) gained were estimated. Costs and outcomes were discounted at 3% annually. One-way deterministic and probabilistic sensitivity analyses (PSA) were conducted.

RESULTS

Over a lifetime horizon, adjuvant olaparib was associated with an additional 1.50 LYs and 1.22 QALYs, and incremental cost of 471,156 Swedish krona (SEK) versus WaW (discounted). The resulting ICER was 385,183SEK per QALY gained for olaparib versus WaW. ICERs remained below 1,000,000SEK across a range of scenarios, and were consistent across subgroups (hormone receptor [HR]-positive/HER2-negative and triple-negative breast cancer [TNBC]). In PSA, the probability of olaparib being cost effective at 1,000,000SEK per QALY was 99.8%.

CONCLUSIONS

At list price, adjuvant olaparib is a cost-effective alternative to WaW in patients with gBRCA1/2-mutated, high-risk, HER2-negative eBC in Sweden.

Seize the engine: Emerging cell cycle targets in breast cancer

Breast cancer arises from a series of molecular alterations that disrupt cell cycle checkpoints, leading to aberrant cell proliferation and genomic instability. Targeted pharmacological inhibition of cell cycle regulators has long been considered a promising anti-cancer strategy. Initial attempts to drug critical cell cycle drivers were hampered by poor selectivity, modest efficacy and haematological toxicity. Advances in our understanding of the molecular basis of cell cycle disruption and the mechanisms of resistance to CDK4/6 inhibitors have reignited interest in blocking specific components of the cell cycle machinery, such as CDK2, CDK4, CDK7, PLK4, WEE1, PKMYT1, AURKA and TTK. These targets play critical roles in regulating quiescence, DNA replication and chromosome segregation. Extensive preclinical data support their potential to overcome CDK4/6 inhibitor resistance, induce synthetic lethality or sensitise tumours to immune checkpoint inhibitors. This review provides a biological and drug development perspective on emerging cell cycle targets and novel inhibitors, many of which exhibit favourable safety profiles and promising activity in clinical trials.

Emerging systemic therapy options beyond CDK4/6 inhibitors for hormone receptor-positive HER2-negative advanced breast cancer

Endocrine therapy (ET) with cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) is currently the standard first-line treatment for most patients with hormone receptor (HR) positive, human epidermal growth factor receptor (HER2) negative advanced breast cancer. However, resistance to ET and CDK4/6i inevitably ensues. The optimal post-progression treatment regimens and their sequencing continue to evolve in the rapidly changing treatment landscape. In this review, we summarize the mechanisms of resistance to ET and CDK4/6i, which can be broadly classified as alterations affecting cell cycle mediators and activation of alternative signaling pathways. Recent clinical trials have been directed at the targets and pathways implicated, including estrogen and androgen receptors, PI3K/AKT/mTOR and MAPK pathways, tyrosine kinase receptors such as FGFR and HER2, homologous recombination repair pathway, other components of the cell cycle and cell death. We describe the findings from these clinical trials using small molecule inhibitors, antibody-drug conjugates and immunotherapy, providing insights into how these novel strategies may circumvent treatment resistance, and discuss how some have not translated into clinical benefit. The challenges posed by tumor heterogeneity, adaptive rewiring of signaling pathways and dose-limiting toxicities underscore the need to elucidate the latest tumor biology in each patient, and develop treatments with improved therapeutic index in the era of precision medicine.

Adjuvant olaparib in the subset of patients from Japan with BRCA1- or BRCA2-mutated high-risk early breast cancer from the phase 3 OlympiA trial

BACKGROUND

The efficacy and safety of olaparib compared with placebo in the subset of patients from Japan in the phase 3 OlympiA trial (NCT02032823) are reported here and contextualized with reference to the global OlympiA population.

METHODS

Patients with germline BRCA1 and/or BRCA2 pathogenic variants and HER2-negative, high-risk early breast cancer who had received neoadjuvant or adjuvant chemotherapy and completed local treatment were eligible. Patients were randomized 1:1 to receive olaparib or placebo for 1 year.

PRIMARY ENDPOINT

invasive disease-free survival (IDFS). Secondary endpoints: distant disease-free survival (DDFS), overall survival (OS), and safety. Data are reported from the first pre-specified interim analysis (data cut-off [DCO] March 27, 2020) and the second, event driven, pre-specified interim analysis of OS (DCO July 12, 2021) in patients from Japan.

RESULTS

140 patients were randomized in Japan (olaparib, n = 64; placebo, n = 76). At the first pre-specified interim analysis (median follow-up: 2.9 years), hazard ratios (HRs) for adjuvant olaparib compared with placebo were 0.5 for IDFS (95% confidence interval [CI] 0.18-1.24) and 0.41 for DDFS (95% CI 0.11-1.16). At the second pre-specified interim analysis of OS, three deaths occurred in the olaparib group versus six deaths in the placebo group (HR, 0.62 [95% CI 0.13-2.36]). Findings were consistent with those for the global population. No new safety signals were observed.

CONCLUSIONS

While this analysis in a Japanese subset of patients was not powered to detect population-related treatment differences, efficacy and safety analysis results were consistent with the global OlympiA population, suggesting the findings from the global study are generalizable to clinical practice in Japan.

Progress and prospects in research and clinical practice of hormone receptor-positive, HER-2-negative breast cancer with BRCA1/2 mutations

Breast cancer (BC) is a heterogeneous disease that is the most common cancer in women worldwide. However, precise subtyping and corresponding treatments have improved patient outcomes. Hormone receptor (HR)-positive, human epidermal growth factor receptor type 2 (HER2)-negative (HR+/HER2-) BC with BRCA1 and/or BRCA2 mutations (BRCA1/2m) is a unique BC subset with dual drivers: homologous recombination deficiency and hormone receptor signaling. Wild-type BRCA1/2 suppresses estrogen receptor-mediated signaling. Loss-of-function mutations in BRCA1/2 release estrogen receptor suppression, leading to reduced sensitivity to endocrine therapy. Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPis) exert antitumor effects against this subtype and can be used in combination with endocrine therapy. Although PARPis have been evaluated in metastatic triple-negative breast cancer, their efficacy against HR+/HER2- BC has not been clearly established. The present review summarizes recent advances and prospects in the progress of the HR+/HER2-/BRCA1/2m subgroup. As such, this article provides theoretical guidance for future research and promotes the use of PARPis for the treatment of HR+/HER2-/BRCA1/2m BC.

Beyond PARP Inhibitors in Advanced Breast Cancer Patients with Germline BRCA1/2 Mutations: Focus on CDK4/6-Inhibitors and Data Review on Other Biological Therapies

We explored the outcomes of germline BRCA1/2 pathogenic/likely pathogenic variants (PVs/LPVs) in the endocrine-sensitive disease treated with first-line standard of care cyclin-dependent kinase 4/6 (CDK4/6) inhibitors. Three studies retrospectively showed a reduction in the overall survival (OS) and progression-free survival (PFS) in gBRCA1/2m patients compared to both the germinal BRCA1/2 wild type (gBRCA1/2wt) and the untested population. Regarding the efficacy of PI3Kα inhibitors, there are no subgroups or biomarker analyses in which germinal BRCA status was explored. However, the biological interactions between the PIK3CA/AKT/mTOR pathway and BRCA1/2 at a molecular level could help us to understand the activity of these drugs when used to treat BC in BRCA1/2 PVs/LPVs carriers. The efficacy of trastuzumab deruxtecan (T-DXd), an antibody-drug conjugate (ADC) targeting HER2 for HER2-low and HER2-positive (HER2+) BC, has been increasingly described. Unfortunately, data on T-DXd in HER2+ or HER2-low metastatic BC harboring germinal BRCA1/2 PVs/LPVs is lacking. Including germinal BRCA1/2 status in the subgroup analysis of the registration trials of this ADC would be of great interest, especially in the phase III trial DESTINY-breast04. This trial enrolled patients with HER2-negative (HER2-) and both HR+ and HR- metastatic disease, which can now be categorized as HER2-low. The HER2-low subgroup includes tumors that were previously classified as triple negative, so it is highly likely that some women were germline BRCA1/2 PVs/LPVs carriers and this data was not reported. Germline BRCA1/2 status will be available for a higher number of individuals with BC in the near future, and data on the prognostic and predictive role of these PVs/LPVs is needed in order to choose the best treatment options.

Efficacy of front-line treatment for hormone receptor-positive HER2-negative metastatic breast cancer with germline BRCA1/2 mutation

BACKGROUND

Efficacy of endocrine therapy in HR+/HER2- metastatic breast cancer could differ depending on the presence of BRCA1/2 germline mutation.

METHODS

The ESME metastatic breast cancer platform (NCT03275311) is a French real world database. Multivariable models including a time-varying approach and landmark analyses assessed the association between time-dependent gBRCA status (categorised as gBRCAm, gBRCAwt (wild type), and untested), overall survival (OS), and first-line progression-free survival (PFS1).

RESULTS

A total of 170 patients were gBRCAm carriers, 676 gBRCAwt, and 12,930 were untested at baseline. In the multivariable analysis, gBRCAm carriers overall had a lower OS compared to gBRCAwt (adjusted HR [95% CI] 1.26 [1.03-1.55]). gBRCAm patients treated with front-line endocrine therapy had lower adjusted OS (adjusted HR [95% CI] = 1.54 [1.03-2.32]) and PFS1 (adjusted HR [95% CI] 1.58 [1.17-2.12]) compared to gBRCAwt patients. However, for patients who received frontline chemotherapy, neither OS nor PFS1 differed between gBRCAm carriers and the other groups (HR versus gBRCAwt for OS: 1.12 [0.88-1.41], p = 0.350; PFS1: 1.09 [0.90-1.31], p = 0.379).

CONCLUSION

In this large cohort of HR+/HER2- MBC patients treated in a pre-CDK4/6 inhibitors era, gBRCAm status was associated with a lower OS and lower PFS following first-line endocrine therapy, but not following first-line chemotherapy.

Post-CDK 4/6 Inhibitor Therapy: Current Agents and Novel Targets

Front-line therapy for advanced and metastatic hormone receptor positive (HR+), HER2 negative (HER-) advanced or metastatic breast cancer (mBC) is endocrine therapy with a CDK4/6 inhibitor (CDK4/6i). The introduction of CDK4/6i has dramatically improved progression-free survival and, in some cases, overall survival. The optimal sequencing of post-front-line therapy must be personalized to patients' overall health and tumor biology. This paper reviews approved next lines of therapy for mBC and available data on efficacy post-progression on CDK4/6i. Given the success of endocrine front-line therapy, there has been an expansion in therapies under clinical investigation targeting the estrogen receptor in novel ways. There are also clinical trials ongoing attempting to overcome CDK4/6i resistance. This paper will review these drugs under investigation, review efficacy data when possible, and provide descriptions of the adverse events reported.

Overall survival in the OlympiA phase III trial of adjuvant olaparib in patients with germline pathogenic variants in BRCA1/2 and high risk, early breast cancer

BACKGROUND

The randomized, double-blind OlympiA trial compared 1 year of the oral poly(adenosine diphosphate-ribose) polymerase inhibitor, olaparib, to matching placebo as adjuvant therapy for patients with pathogenic or likely pathogenic variants in germline BRCA1 or BRCA2 (gBRCA1/2pv) and high-risk, human epidermal growth factor receptor 2-negative, early breast cancer (EBC). The first pre-specified interim analysis (IA) previously demonstrated statistically significant improvement in invasive disease-free survival (IDFS) and distant disease-free survival (DDFS). The olaparib group had fewer deaths than the placebo group, but the difference did not reach statistical significance for overall survival (OS). We now report the pre-specified second IA of OS with updates of IDFS, DDFS, and safety.

PATIENTS AND METHODS

One thousand eight hundred and thirty-six patients were randomly assigned to olaparib or placebo following (neo)adjuvant chemotherapy, surgery, and radiation therapy if indicated. Endocrine therapy was given concurrently with study medication for hormone receptor-positive cancers. Statistical significance for OS at this IA required P < 0.015.

RESULTS

With a median follow-up of 3.5 years, the second IA of OS demonstrated significant improvement in the olaparib group relative to the placebo group [hazard ratio 0.68; 98.5% confidence interval (CI) 0.47-0.97; P = 0.009]. Four-year OS was 89.8% in the olaparib group and 86.4% in the placebo group (Δ 3.4%, 95% CI -0.1% to 6.8%). Four-year IDFS for the olaparib group versus placebo group was 82.7% versus 75.4% (Δ 7.3%, 95% CI 3.0% to 11.5%) and 4-year DDFS was 86.5% versus 79.1% (Δ 7.4%, 95% CI 3.6% to 11.3%), respectively. Subset analyses for OS, IDFS, and DDFS demonstrated benefit across major subgroups. No new safety signals were identified including no new cases of acute myeloid leukemia or myelodysplastic syndrome.

CONCLUSION

With 3.5 years of median follow-up, OlympiA demonstrates statistically significant improvement in OS with adjuvant olaparib compared with placebo for gBRCA1/2pv-associated EBC and maintained improvements in the previously reported, statistically significant endpoints of IDFS and DDFS with no new safety signals.

The Role of CDK Pathway Dysregulation and Its Therapeutic Potential in Soft Tissue Sarcoma

Soft tissue sarcomas (STSs) are tumors that are challenging to treat due to their pathologic and molecular heterogeneity and their tumor biology that is not yet fully understood. Recent research indicates that dysregulation of cyclin-dependent kinase (CDK) signaling pathways can be a strong driver of sarcogenesis. CDKs are enzyme forms that play a crucial role in cell-cycle control and transcription. They belong to the protein kinases group and to the serine/threonine kinases subgroup. Recently identified CDK/cyclin complexes and established CDK/cyclin complexes that regulate the cell cycle are involved in the regulation of gene expression through phosphorylation of critical components of transcription and pre-mRNA processing mechanisms. The current and continually growing body of data shows that CDKs play a decisive role in tumor development and are involved in the proliferation and growth of sarcoma cells. Since the abnormal expression or activation of large numbers of CDKs is considered to be characteristic of cancer development and progression, dysregulation of the CDK signaling pathways occurs in many subtypes of STSs. This review discusses how reversal and regulation can be achieved with new therapeutics and summarizes the current evidence from studies regarding CDK modulation for STS treatment.

Functions of Breast Cancer Predisposition Genes: Implications for Clinical Management

Approximately 5–10% of all breast cancer (BC) cases are caused by germline pathogenic variants (GPVs) in various cancer predisposition genes (CPGs). The most common contributors to hereditary BC are BRCA1 and BRCA2, which are associated with hereditary breast and ovarian cancer (HBOC). ATM, BARD1, CHEK2, PALB2, RAD51C, and RAD51D have also been recognized as CPGs with a high to moderate risk of BC. Primary and secondary cancer prevention strategies have been established for HBOC patients; however, optimal preventive strategies for most hereditary BCs have not yet been established. Most BC-associated CPGs participate in DNA damage repair pathways and cell cycle checkpoint mechanisms, and function jointly in such cascades; therefore, a fundamental understanding of the disease drivers in such cascades can facilitate the accurate estimation of the genetic risk of developing BC and the selection of appropriate preventive and therapeutic strategies to manage hereditary BCs. Herein, we review the functions of key BC-associated CPGs and strategies for the clinical management in individuals harboring the GPVs of such genes.

Management Strategies of Breast Cancer Patients with BRCA1 and BRCA2 Pathogenic Germline Variants

Most of breast cancer cases are sporadic; however, 15–20% are associated with family history, and some are inherited. Among those, deleterious mutations in BRCA1 and BRCA2 tumor suppressor genes are the most commonly encountered pathogenic germline variants (PGVs). Given the availability and affordability of multi-gene panel sequencing technologies, testing for PGVs is commonly practiced. With our enhanced understanding of cancer genetics and specific molecular alterations, the better acceptance of risk-directed screening and prevention, and the recent introduction of novel targeted therapies, management of BRCA-positive breast cancers is taking a new direction, focusing more on risk-reducing interventions, including mastectomy and salpingo-oophorectomy, and incorporating special treatment regimens, including platinum-based chemotherapy, and the recently-introduced PARP (poly (ADP)-ribose polymerase) inhibitors. Given the recent advances in reproductive technology and molecular medicine, younger women with PGVs may have the option of embryo selection through preimplantation genetic testing and diagnosis, thus preventing the potential transmission of the implicated genes to the next generations. In this review, we cover the clinical implications of identifying a pathogenic germline mutation in BRCA1 and BRCA2 genes in breast cancer patients, and their relatives, across the continuum of care – from cancer prevention and early detection, through active treatment and up to survivorship issues.