Recent advances in nanoscale targeted therapy of HER2-positive breast cancer.

Breast cancer is considered as the second major cause of death among women with a high mortality rate worldwide. The exceptionally fast rate of metastasis, the emergence of drug-resistant mechanisms, and the occurrence of inadvertent side effects by cytotoxic chemotherapies often make conventional chemotherapy and immunotherapy treatments ineffective. Similar to other solid tumours, breast cancer can develop unique cellular and molecular characteristics forming an atypical permissive tumour microenvironment (TME). Due to the unique features of TME, cancer cells can further proliferate and coadapt with the stromal cells and evade immunosurveillance. Breast cancer cells aberrantly abundantly express various pieces of molecular machinery (the so-called oncomarkers) in favour of their survival, progression, metastasis, and further invasion. Such overexpressed oncomarkers can be exploited in the detection and targeted therapy of cancer. Among breast cancer oncomarkers, epidermal growth factor receptors, particularly HER2, are considered as clinically valid molecular targets not only for the thorough diagnosis but also for the targeted therapy of the disease using different conventional and advanced nanoscale treatment modalities. This review aims to elaborate on the recent advances in terms of targeted therapy of HER2-positive breast cancer, and discuss various types of multifunctional nanomedicines/theranostics, and antibody-/aptamer-drug conjugates.