**Abstract**

Breast cancer (BC) is one of the most frequently occurring diseases with high morbidity and mortality rates in the world today. BC cells live under stress with altered pathway signaling, chromosome and microsatellite instability, aneuploidy, hypoxia, low pH, and low nutrient conditions. In order to survive and reproduce in these stressful environments, BC cells rapidly undergo adaptive mutations, rearrange their chromosomes, and repress tumor suppressor genes while inducing oncogene activities that cause the natural selection of cancer cells and result in heterogeneous cancer cells in the tumor environment. Unfortunately, these genetic alterations result in aggressive BC cells that can not only proliferate aggressively but also migrate and invade the other tissues in the body to form secondary tumors. In this review, molecular mechanisms of metastasis of BC subtypes are discussed.

**Keywords:** breast cancer, metastasis, heterogeneity, luminal A and B, TNBC, HER2+
