Breast cancer is the most common cancer in women and the second leading cause of cancer‐related deaths after lung cancer. Metastasis of the central nervous system is a terrible event for breast cancer patients, affecting their survival and quality of life. Compared with hormone receptor‐positive/human epidermal growth factor receptor 2‐negative breast cancer patients, brain metastases are more likely to affect patients with triple‐negative breast cancer and human epidermal growth factor receptor 2‐positive breast cancer. The treatment of breast cancer has improved greatly in the last two decades. However, brain metastases from breast cancer remain the leading cause of morbidity and mortality. Patients with breast cancer brain metastasis have been in an inferior position due to the lack of clinical research in this field, and they are often explicitly excluded from almost all clinical trials. The occurrence and progression of brain metastases will result in severe cognitive impairment and adverse physical consequences, so we must have a good understanding of the molecular mechanisms of breast cancer brain metastasis. In this article, we have retrieved the latest literature of molecules and pathways associated with breast cancer brain metastasis, summarized common therapy strategies, and discussed the prospects and clinical implications of targeting the molecules involved.

Breast cancer (BC) is the most common malignancy among females worldwide, and high resistance to drugs and metastasis rates are the leading causes of death in BC patients. Releasing anti-cancer drugs precisely to the tumor site can improve the efficacy and reduce the side effects on the body. Natural polymers are attracting extensive interest as drug carriers in treating breast cancer. Hyaluronic acid (HA) is a natural polysaccharide with excellent biocompatibility, biodegradability, and non-immunogenicity and is a significant component of the extracellular matrix. The CD44 receptor of HA is overexpressed in breast cancer cells and can be targeted to breast tumors. Therefore, many researchers have developed nano drug delivery systems (NDDS) based on the CD44 receptor tumor-targeting properties of HA. This review examines the application of HA in NDDSs for breast cancer in recent years. Based on the structural composition of NDDSs, they are divided into HA NDDSs, Modified HA NDDSs, and HA hybrid NDDSs.

Breast cancer is one of the most prevalent types of cancer in women and contributes to 32% of all female cancer cases. Cathepsins, a family of proteins, are known to have a critical role in human cancers. However, previous studies on the systematic analysis of the role of cathepsin family members in breast cancer are limited. The aim of the present study was to identify biological markers to predict prognosis and treatment response of breast cancer patients, as well as to elucidate novel therapeutic targets. The present study analyzed the expression of six members of cathepsin family, including cathepsins B, G, D, K, L and V in 188 breast cancer tissue specimens using immunohistochemistry. The data showed that all members of the tested cathepsin families featured cytoplasmic staining. Notably, expression of cathepsin L was associated with advanced tumor stages, while cathepsins B and K expression levels were associated with positive estrogen receptor expression; in addition, cathepsin K expression was also demonstrated to be associated with progesterone receptor expression. Cathepsins V and D expression levels were found to be associated with breast cancer metastasis, while the expression levels of cathepsins B and D were associated with poor disease‑free survival in breast cancer patients. In addition, univariate analysis demonstrated that breast cancer metastasis to the bone and the expression of cathepsin B protein were associated with poor disease‑free survival. In conclusion, the results of the present study indicated that the altered expression of cathepsins, in particular cathepsins B and D, contributed to the progression of breast cancer and poor disease-free survival in breast cancer patients.

Purpose: The Chinese bridging study PUFFIN (NCT02896855) aimed to assess consistency of efficacy with CLEOPATRA (NCT00567190), investigating pertuzumab with trastuzumab and docetaxel versus placebo, trastuzumab, and docetaxel in patients with previously untreated HER2-positive locally recurrent or metastatic breast cancer. Methods: Patients were randomized 1:1, stratified by visceral/non-visceral disease and hormone receptor status. The primary endpoint was investigator-assessed progression-free survival (PFS). Secondary endpoints included objective response rate (in patients with measurable baseline disease), overall survival, and safety. The consistency threshold for PFS (hazard ratio [HR] < 0.81) (maintaining ≥ 50% of the risk reduction determined in CLEOPATRA [HR 0.62]) determined the target sample size (n = 240). Results: Two hundred forty-three patients were randomized. Median PFS was 14.5 months in the pertuzumab arm (95% confidence interval [CI] 12.5, 18.6) and 12.4 months in the placebo arm (95% CI 10.4, 12.7) in the intention-to-treat population (HR: 0.69 [95% CI 0.49, 0.99]). Objective responses were recorded in 83/105 (79.0%) and 67/97 (69.1%) patients, respectively. Grade ≥ 3 adverse events (70.5% and 69.2%, respectively) and serious adverse events (19.7% and 19.2%, respectively) were similar across both arms. No heart failure cases or symptomatic left ventricular ejection fraction declines were reported. Conclusions: PUFFIN met its primary objective. Overall, efficacy data were consistent with CLEOPATRA. Safety was consistent with the known pertuzumab safety profile. PUFFIN adds to the totality of data with pertuzumab in previously untreated HER2-positive locally recurrent or metastatic breast cancer and supports the favorable benefit–risk profile of pertuzumab in Chinese patients Trial registration: ClinicalTrials.gov, NCT02896855, registered 7 September 2016