expression of the following hormone receptors: estrogen (ER), progesterone (PR) and human epidermal growth factor (HER2). Accordingly, the following four subtypes of breast cancer are widely recognized: luminal A, luminal B, HER2-positive, and triple-negative. With the recent advances in cancer research, and an increased molecular understanding of breast cancer, the current clinical model for classification of breast cancer may be benefit from the addition of several molecular markers such as miRNAs (let-7, miR-155, miR-150, miR-153) and mutations (p53, BRCA 1 and 2 genes). This chapter provides an overview of the characteristics of these four subtypes of breast cancer.

Breast cancer represents 16% of all malignant tumors diagnosed and is the leading cause of mortality in women worldwide. While significant advances in the diagnosis and treatment of breast cancer have been made over the years, the management of advanced stages of the disease and treatment-related adverse events continue to be a challenge. There is a need to develop tools for target-specific delivery of drugs to improve efficiency and decrease non-specific drug-induced Note to the Reader: This chapter is part of the book Breast Cancer (ISBN: 978-0-6453320-3-2), scheduled for publication in July 2022. The book is being published by Exon Publications,