PTPN11 and breast cancer: Relevant scholars have selected breast cancer cell lines MDA-MB-231 cells and BT549 cells as the research objects, by constructing recombinant plasmids (shSHP2-NC1, shSHP2-NC3) that reduce the expression of SHP2 stably and small interfering RNA fragments that reduce the expression of SHP2 transiently (SiSHP2-1#, siSHP2-2#), analyzing the effect of downregulation of SHP2 protein level on ERK signaling pathway.