Deregulation of cell cycle, via cyclin D/CDK/pRb pathway, is frequently observed in breast cancer lending support to the development of drugs targeting the cell cycle control machinery, like the inhibitors of the cycline-dependent kinases (CDK) 4 and 6. Up to now, three CDK4/6 inhibitors have been approved by FDA for the treatment of hormone receptor-positive (HR+), HER2-negative metastatic breast cancer. These agents have been effective in improving the clinical outcomes, but the development of intrinsic or acquired resistance can limit the efficacy of these treatments. Clinical and translational research is now focused on investigation of the mechanism of sensitivity/resistance to CDK4/6 inhibition and novel therapeutic strategies aimed to improve clinical outcomes. This review summarizes the available knowledge regarding CDK4/6 inhibitor, the discovery of new biomarkers of response, and the biological rationale for new combination strategies of treatment.

The introduction of CDK4/6 inhibitors in combination with endocrine therapy (ET) represents the most relevant advance in the management of hormone receptor (HR) positive, HER2-negative metastatic breast cancer over the last few years. This meta-analysis of randomized controlled trials (RCTs) is aimed to better characterize the efficacy of CDK4/6 inhibitors in some relevant subgroups and to test heterogeneity between different compounds with a particular focus on their ability to improve overall survival (OS). Pooled estimates of hazard ratios (HRs) were computed for progression-free survival (PFS), OS, and objective response rate (ORR) analysis in predefined subgroups to better understand treatment effect concerning specific patients’ characteristics. To estimate the absolute benefit in terms of PFS, pooled survival curves were generated by pooling the data of all trials. A total of eight RCTs were included. Adding a CDK4/6 inhibitor to ET is beneficial in terms of PFS, irrespective of the presence or not of visceral metastases, the number of metastatic sites, and the length of the treatment-free interval (TFI). The addition of CDK4/6 inhibitors produces a significant OS improvement, both in aromatase inhibitor (AI)-sensitive (HR 0.75, 95% CI) and AI-resistant patients (HR 0.77, 95% CI [0.67–0.89]). Pooled data from each single drug show that palbociclib remains the only class member not showing a statistically significant HR for OS (HR 0.83, 95% CI [0.68–1.02]).

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BackgroundMale breast cancer (MBC) is rare. Given the paucity of randomized trials, treatment is generally extrapolated from female breast cancer guidelines.MethodsThis is a retrospective analysis of all male patients presenting with MBC at the Department of Oncology at University Federico II of Naples between January 1989 and January 2014. We recorded the following data: baseline characteristics (age, height, weight, body mass index, risk factors, family history), tumor characteristics (side affected, stage, histotype, hormonal and HER2 status, and Ki-67 expression), treatment (type of surgery, chemotherapy, endocrine therapy, and/or radiotherapy), BRCA1/2 mutation status (if available), other tumors, and long-term survival.ResultsForty-seven patients were analyzed. Median age was 62.0 [55.0–72.0]. Among risk factors, obesity and family history of breast cancer were associated with 21 % and 30 % of MBC cases, respectively. The majority of tumors were diagnosed at an early stage: stage I (34.0 %) and stage II (44.7 %). Infiltrating ductal carcinoma was the most frequent histologic subtype (95.8 %). Hormone receptors were generally positive (88.4 % of cases were Estrogen receptor [ER] positive and 81.4 % Progesteron receptor [PgR] positive). Human epidermal growth factor receptor 2 (HER2) was positive in 26.8 % of cases; 7.0 % of MBCs were triple negative. The tumor had high proliferation index (Ki67 ≥ 20 %) in 64.7 %. Surgery was predominantly mastectomy (85.1 %), whereas quadrantectomy was performed in 14.9 % of patients. Adjuvant chemotherapy was administered to 70.7 % of patients, endocrine therapy to 90.2 %, trastuzumab to 16.7 % and radiotherapy to 32.6 %. BRCA status was available for 17 patients: 10 wild-type, 1 BRCA1 carrier, 5 BRCA2 carriers, 1 unknown variant sequence. The overall estimated long-term survival was about 90 % at 5 years, 80 % at 10 years and 70 % at 20 years. Patients carrying a BRCA mutation had a significantly lower survival than patients with wild-type BRCA (p = 0.04).ConclusionsLong-term survival was high in MBC patients referred to our clinical unit. Survival was poorer in BRCA-mutated patients than in patients with wild-type BRCA.