B2M and breast cancer: Although increased β2-M serum levels in patients with breast cancer have been previously reported [6, 9, 12], the clinical value of β2-M as a prognostic factor and predictor of survival, and its mechanism in patients with breast cancer, need further study, since breast cancer has different molecular subtypes [14] and patients with the same clinical stages and pathological types of breast cancer, treated with same scheme, have different therapeutic and prognostic effects.