Systemic Treatment Strategies for Patients with Hereditary Breast Cancer Syndromes

Hereditary breast cancer syndromes are associated with an increased risk of breast cancer and constitute a unique patient population, making up approximately 5%-10% of breast cancer cases in the United States. By virtue of the germline mutations that define these syndromes, invasive breast cancers in these patients have unique mechanisms that can be rationally targeted for therapeutic opportunities distinct from standard of care treatments in nongermline mutation associated breast cancers. This review intends to describe existing data on several of the most common hereditary breast cancer syndromes, including BRCA-related breast cancer syndrome, Li-Fraumeni syndrome, Cowden syndrome, Peutz-Jeghers syndrome, and hereditary diffuse gastric cancer syndrome, specifically focusing on rational therapeutics utilized in these distinct patient subgroups and completed or ongoing clinical trials evaluating their efficacy. By exploiting the distinct biologic features associated with these syndromes, tailored treatment strategies have the potential for improved efficacy and lower toxicity. Knowledge of the emergence of these targeted cancer therapies is critical for appropriate management in these patients, extending beyond treatment to highlight the need for appropriate genetic screening to allow for early recognition of these patients and therefore appropriate treatment.

IMPLICATIONS FOR PRACTICE

Molecular testing allows for identification of germline mutations that place individuals at high risk for breast cancer and that are associated with distinct histopathology and molecular characteristics that define the invasive breast cancer cases that these patients develop. These unique characteristics may ultimately provide rational targets for systemic treatments with improvements in both morbidity and efficacy. Identification of patients with these germline mutations is important for not only appropriate screening and prophylaxis, but knowledge of therapies specifically targeting several of the most common hereditary breast cancer syndromes is essential to ensure appropriate treatment of invasive breast cancers in these patients.

Therapeutic potential of PARP inhibitors for metastatic breast cancer

Increasing understanding of the cellular aberrations inherent to cancer cells has allowed the development of therapies to target biological pathways, an important step towards individualization of breast cancer therapy. The clinical development of poly(ADP-ribose) polymerase (PARP) inhibitors, with their novel and selective mechanism of action, are an example of this strategy. PARP plays a key role in DNA repair mechanisms, particularly the base excision repair pathway. Initially developed as inhibitors able to enhance the cytotoxicity of radiation and certain DNA-damaging agents, they have more recently been shown to have single-agent activity in certain tumors. Inhibition of PARP in a DNA repair-defective tumor can lead to gross genomic instability and cell death by exploiting the paradigm of synthetic lethality. Several studies have evaluated the role of PARP inhibitors for treatment of breast cancer, particularly in the context of BRCA-mutated and triple-negative breast cancers. In addition, inhibition of PARPs repair functions for chemotherapy-induced DNA lesions has been shown to potentiate the effect of some chemotherapy regimens. This article discusses the current understanding of PARP inhibition as a treatment for metastatic breast cancer, evidence from clinical trials and addresses its future implications.

Trends and Novel Approaches in Neoadjuvant Treatment of Breast Cancer

Breast cancer is the most prevalent malignant disease in women worldwide. Traditionally, surgical tumour resection was the primary step within the treatment algorithm of early stage disease; systemic therapy in order to reduce the rate of systemic recurrences followed. National Surgical Adjuvant Breast and Bowel Project (NSABP) trial B-18 found that pre- and postoperative administration of chemotherapy was equally effective. This study therefore established neoadjuvant chemotherapy as a valid treatment option, as the breast conservation rate is increased. Modern neoadjuvant regimens encompassing anthracyclines and taxanes yield pathological complete response (pCR) rates of around 20%, with higher efficacy observed in triple-negative tumours. The antibody trastuzumab is the first targeted agent established in neoadjuvant regimens for the treatment of Her2-positive breast cancer, as it raised pCR rates up to 50%. Novel approaches are aiming to increase the efficacy of neoadjuvant therapy. Inclusion of capecitabine might further increase pCR rates in selected patients, although data are not unanimous throughout the respective clinical trials. In patients harbouring BRCA-1 germline mutations, platinum derivatives are apparently promising. Novel Her2-targeted agents such as lapatinib and pertuzumab are currently under investigation in several clinical trials, while the role of bevacizumab, a monoclonal antibody inhibiting angiogenesis, awaits future clarification.