Breast cancer that grows anywhere in the breast is dangerous and does not vary in danger depending on the location. However, breast cancer that has metastasized to distant organs is most dangerous when it has metastasized to the brain. Breast cancer is defined as a malignant tumor that develops when the epithelial or ductal tissue of the lobules of the breast proliferates out of control. The tumor can occur in any location of the breast, and there is no essential difference in the degree of danger from one location to another. The common location is the upper outer quadrant of the breast, i.e., near the armpit. Early stage of breast cancer may show symptoms such as breast lumps and enlarged lymph nodes in the armpit. In the middle and late stages of breast cancer, the tumor can be metastasized through lymph nodes as well as blood line, and the common sites of metastasis are lungs, liver, bones, brain, etc. Metastasis is usually more dangerous, and the most dangerous is brain metastasis. Brain metastasis can easily compress the brain stem and other important life centers, and the survival time in this case is usually only 3~6 months or even shorter. Once diagnosed with breast cancer, patients should actively cooperate with the doctor’s treatment plan to minimize the risk.