Chemotherapy is a key treatment against recurrence and metastasis of breast cancer. Generally, in situ cancer does not metastasize, so chemotherapy is not necessary. However, for most patients with invasive breast cancer, chemotherapy is necessary. Depending on the current technology, a subset of patients can be screened to avoid chemotherapy. Most patients with immunohistochemistry results of ER(+), PR(+), Her2(-), Ki67<14%, i.e. tumor molecular typing of Luminal A, do not need chemotherapy. The reason for saying most but not all is that some of these patients have other indicators that are not good and need to be considered for chemotherapy.