MKI67 and breast cancer: The overexpression of circ0000199 is significantly associated with tumor size, TNM stage, and Ki-67 level in patients with breast cancer.267 Higher levels of circPRMT5, circHIPK3, circ001569, and circ0000199 predict poor prognosis in breast cancer.263,264,266,267 circ0000199 can affect tumor cell tolerance of chemotherapy via suppression of the PI3K/AKT/mTOR pathway and activation of the miR-206/miR-613 axis.267 circ0000199 also enhances cell proliferation, migration, and invasion in breast cancer.