CDK4/6 inhibition in breast cancer: current practice and future directions

The cyclin D/cyclin-dependent kinases 4 and 6 (CDK4/6)-retinoblastoma protein (RB) pathway plays a key role in the proliferation of both normal breast epithelium and breast cancer cells. A strong rationale for inhibiting CDK4/6 in breast cancers has been present for many years. However, potent and selective CDK4/6 inhibitors have only recently become available. These agents prevent phosphorylation of the RB tumor suppressor, thereby invoking cancer cell cycle arrest in G1. CDK4/6 inhibitors have transited rapidly from preclinical studies to the clinical arena, and three have already been approved for the treatment of advanced, estrogen receptor (ER)-positive breast cancer patients on account of striking clinical trial results demonstrating substantial improvements in progression-free survival. ER-positive breast cancers harbor several molecular features that would predict their sensitivity to CDK4/6 inhibitors. As physicians gain experience with using these agents in the clinic, new questions arise: are CDK4/6 inhibitors likely to be useful for patients with other subtypes of breast cancer? Are there other agents that could be effectively combined with CDK4/6 inhibitors, beyond endocrine therapy? Is there a rationale for combining CDK4/6 inhibitors with novel immune-based therapies? In this review, we describe not only the clinical data available to date, but also the biology of the CDK4/6 pathway and discuss answers to these questions. In particular, we highlight that CDK4 and CDK6 govern much more than the cancer cell cycle, and that their optimal use in the clinic depends on a deeper understanding of the less well characterized effects of these enzymes

International Guidelines for Management of Metastatic Breast Cancer: Can Metastatic Breast Cancer Be Cured?

A distinctive subset of metastatic breast cancer (MBC) is oligometastatic disease, which is characterized by single or few detectable metastatic lesions. The existing treatment guidelines for patients with localized MBC include surgery, radiotherapy, and regional chemotherapy. The European School of Oncology-Metastatic Breast Cancer Task Force addressed the management of these patients in its first consensus recommendations published in 2007. The Task Force endorsed the possibility of a more aggressive and multidisciplinary approach for patients with oligometastatic disease, stressing also the need for clinical trials in this patient population. At the sixth European Breast Cancer Conference, held in Berlin in March 2008, the second public session on MBC guidelines addressed the controversial issue of whether MBC can be cured. In this commentary, we summarize the discussion and related recommendations regarding the available therapeutic options that are possibly associated with cure in these patients. In particular, data on local (surgery and radiotherapy) and chemotherapy options are discussed. Large retrospective series show an association between surgical removal of the primary tumor or of lung metastases and improved long-term outcome in patients with oligometastatic disease. In the absence of data from prospective randomized studies, removal of the primary tumor or isolated metastatic lesions may be an attractive therapeutic strategy in this subset of patients, offering rapid disease control and potential for survival benefit. Some improvement in outcome may also be achieved with optimization of systemic therapies, possibly in combination with optimal local treatmen

Should a Sentinel Node Biopsy Be Performed in Patients with High-Risk Breast Cancer?

A negative sentinel lymph node (SLN) biopsy spares many breast cancer patients the complications associated with lymph node irradiation or additional surgery. However, patients at high risk for nodal involvement based on clinical characteristics may remain at unacceptably high risk of axillary disease even after a negative SLN biopsy result. A Bayesian nomogram was designed to combine the probability of axillary disease prior to nodal biopsy with customized test characteristics for an SLN biopsy and provides the probability of axillary disease despite a negative SLN biopsy. Users may individualize the sensitivity of an SLN biopsy based on factors known to modify the sensitivity of the procedure. This tool may be useful in identifying patients who should have expanded upfront exploration of the axilla or comprehensive axillary irradiation

Aromatase inhibitors as adjuvant therapy for postmenopausal women: a therapeutic advance but many unresolved questions

Adjuvant hormonal therapy for postmenopausal women with early stage breast cancer has become far more complex over the past several years. This commentary reviews the current status of the five major trials evaluating the use of the aromatase inhibitors in the adjuvant setting. The data currently available suggest that the aromatase inhibitors are efficacious either as upfront therapy or after a course of tamoxifen. Ongoing trials will compare these approaches and guide the use of these agents in the years to come

Surveillance Mammography in Older Patients With Breast Cancer—Can We Ever Stop?: A Review

Approximately 4–5% of breast cancer survivors will develop a new ipsilateral or contralateral cancer (“in-breast event”) over the 5 years following diagnosis, and annual surveillance mammography is recommended for those with residual breast tissue. The risk for such in-breast events persists over time, though increasing age at cancer diagnosis and treatment with hormonal therapy are associated with lower risk, and most older breast cancer survivors will ultimately die from non-breast cancer related causes. Specific guidelines for surveillance strategies in older patients are limited. Prospective data on the benefits and harms of surveillance mammography in this population are lacking, and most of the evidence is derived from observational, retrospective data, often in the general population

Poly(ADP-Ribose) Polymerase Inhibition: "Targeted" Therapy for Triple-Negative Breast Cancer

In contrast to endocrine-sensitive and HER2-positive breast cancer, novel agents capable of treating advanced triple negative breast cancer (TNBC) are lacking. PARP (Poly-(adenosine diphosphate [ADP]-ribose) polymerase) inhibitors are emerging as one of the most promising ‘targeted’ therapeutics to treat TNBC, with the intended ‘target’ being DNA repair. PARP's are a family of enzymes involved in multiple cellular processes including DNA repair. TNBC shares multiple clinico-pathologic features with BRCA-mutated breast cancers which harbor dysfunctional DNA repair mechanisms. Investigators hypothesized PARP inhibition, in conjunction with the loss of DNA-repair via BRCA-dependent mechanisms, would result in synthetic lethality and augmented cell death. This hypothesis has borne out in both preclinical models and in clinical trials testing PARP inhibitors in both BRCA-deficient and TNBC. The focus of this review will include an overview of the preclinical rationale for evaluating PARP inhibitors in TNBC, the presumed mechanism of action of this novel therapeutic class, promising results from several influential clinical trials of PARP inhibition in advanced breast cancer (both TNBC and BRCA-deficient), proposed mechanisms of acquired resistance to PARP inhibitors, and, finally, conclude with current challenges and future directions for the development of PARP inhibitors in the treatment of breast cancer

Phase III Trial Evaluating Letrozole As First-Line Endocrine Therapy With or Without Bevacizumab for the Treatment of Postmenopausal Women With Hormone Receptor-Positive Advanced-Stage Breast Cancer: CALGB 40503 (Alliance)

PURPOSE: To investigate whether anti-vascular endothelial growth factor therapy with bevacizumab prolongs progression-free survival (PFS) when added to first-line letrozole as treatment of hormone receptor-positive metastatic breast cancer (MBC). PATIENTS AND METHODS: Women with hormone receptor-positive MBC were randomly assigned 1:1 in a multicenter, open-label, phase III trial of letrozole (2.5 mg orally per day) with or without bevacizumab (15 mg/kg intravenously once every 3 weeks) within strata defined by measurable disease and disease-free interval. This trial had 90% power to detect a 50% improvement in median PFS from 6 to 9 months. Using a one-sided α = .025, a target sample size of 352 patients was planned. RESULTS: From May 2008 to November 2011, 350 women were recruited; 343 received treatment and were observed for efficacy and safety. Median age was 58 years (range, 25 to 87 years). Sixty-two percent had measurable disease, and 45% had de novo MBC. At a median follow-up of 39 months, the addition of bevacizumab resulted in a significant reduction in the hazard of progression (hazard ratio, 0.75; 95% CI, 0.59 to 0.96; P = .016) and a prolongation in median PFS from 15.6 months with letrozole to 20.2 months with letrozole plus bevacizumab. There was no significant difference in overall survival (hazard ratio, 0.87; 95% CI, 0.65 to 1.18; P = .188), with median overall survival of 43.9 months with letrozole versus 47.2 months with letrozole plus bevacizumab. The largest increases in incidence of grade 3 to 4 treatment-related toxicities with the addition of bevacizumab were hypertension (24% v 2%) and proteinuria (11% v 0%). CONCLUSION: The addition of bevacizumab to letrozole improved PFS in hormone receptor-positive MBC, but this benefit was associated with a markedly increased risk of grade 3 to 4 toxicities. Research on predictive markers will be required to clarify the role of bevacizumab in this setting

Physical activity, weight, and outcomes in patients receiving chemotherapy for metastatic breast cancer (C40502/Alliance)

Background: Obesity and inactivity are associated with increased risk of cancer-related and overall mortality in breast cancer, but there are few data in metastatic disease. Methods: Cancer and Leukemia Group B 40502 was a randomized trial of first-line taxane-based chemotherapy for patients with metastatic breast cancer. Height and weight were collected at enrollment. After 299 patients enrolled, the study was amended to assess recreational physical activity (PA) at enrollment using the Nurses\u27 Health Study Exercise Questionnaire. Associations with progression-free survival (PFS) and overall survival (OS) were evaluated using stratified Cox modeling (strata included hormone receptor status, prior taxane, bevacizumab use, and treatment arm). All statistical tests were 2-sided. Results: A total of 799 patients were enrolled, and at the time of data lock, median follow-up was 60 months. At enrollment, median age was 56.7 years, 73.1% of participants had hormone receptor-positive cancers, 42.6% had obesity, and 47.6% engaged in less than 3 metabolic equivalents of task (MET) hours of PA per week (\u3c1 hour of moderate PA). Neither baseline body mass index nor PA was statistically significantly associated with PFS or OS, although there was a marginally statistically significant increase in PFS (hazard ratio = 0.83, 95% confidence interval = 0.79 to 1.02; Conclusions: In a trial of first-line chemotherapy for metastatic breast cancer, rates of obesity and inactivity were high. There was no statistically significant relationship between body mass index and outcomes. More information is needed regarding the relationship between PA and outcomes

Blood Vessel Morphologic Changes Depicted with MR Angiography during Treatment of Brain Metastases: A Feasibility Study

To prospectively determine a) if magnetic resonance angiograms (MRA) can detect intracranial vascular morphological changes during treatment of brain metastases from breast cancer, and b) if serial, quantitative vessel tortuosity measurements might predict tumor treatment response in advance of traditional methods

Accrual of Older Patients With Breast Cancer to Alliance Systemic Therapy Trials Over Time: Protocol A151527

Despite increasing awareness of accrual challenges, it is unknown if accrual of older patients to breast cancer treatment trials is improving