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OBJECTIVE: To probe into the effects of walnut green husk extract on proliferation, apoptosis and epidermal growth factor receptor (EGFR) / mitogen activated protein kinase (MAPK) signaling pathway of breast cancer MCF-7 cells. METHODS: Cell counting kit-8 (CCK-8) was used to screen the proper concentration of walnut husk extract interfering with breast cancer MCF-7 cells. The breast cancer MCF-7 cells were divided into the blank control group, positive control group, walnut husk husk extract low concentration group, walnut green husk extract high concentration group, walnut green husk extract high concentration + EGFR agonist (NSC228155) group. CCK-8 and colony formation experiment were used to detect cell proliferation in each group. TUNEL method and flow cytometry were used to detect cell apoptosis in each group. Western blot was used to detect the expression levels of proliferation, apoptosis and EGFR/ MAPK signaling pathway related proteins of cells in each group. RESULTS: When the concentration of walnut green husk extract was ≥20 μg/ mL, the cell proliferation rate decreased significantly, 20 μg/ mL and 40 μg/ mL were selected as the walnut green husk extract low and high concentration treatment, respectively. Compared with the blank control group, the cell proliferation rate, the number of cell colonies, the expression levels of CyclinD1, proliferating cell nuclear antigen (PCNA) and B cell lymphoma-2 (Bcl-2) protein, the ratio of phosphorylated-EGFR (p-EGFR) / EGFR, phosphorylated extracellular signal-regulated kinase (p-ERK) / extracellular signal-regulated kinase ( ERK ), phosphorylated-p38 MAPK ( p-p38 MAPK ) / p38 MAPK and phosphorylated c-Jun amino-terminal protein kinase (p-JNK) / c-Jun amino-terminal protein kinase (JNK) protein in the positive control group, the walnut green husk extract low concentration group and high concentration group decreased significantly, and the rate of TUNEL positive cells, the apoptosis rate, the expression level of Bcl-2 related X protein (Bax) increased significantly, with statistically significant differences (P<0. 05). Compared with the walnut green husk extract low concentration group, the cell proliferation rate, the number of cell colonies, the expression levels of CyclinD1, PCNA and Bcl-2 protein, the ratio of p-EGFR/ EGFR, p-ERK/ ERK, p-p38 MAPK/ p38 MAPK and p-JNK/ JNK protein in the walnut green husk extract high concentration group decreased, and the rate of TUNEL positive cells, the apoptosis rate, the expression level of Bax protein increased, with statistically significant differences (P<0. 05). There was no significant difference in the above indicators between the walnut green husk extract high concentration group and the positive control group (P >0. 05). Compared with the walnut green husk extract high concentration group, the cell proliferation rate, the number of cell colonies, the expression levels of CyclinD1, PCNA and Bcl-2 protein, the ratio of p-EGFR/ EGFR, p-ERK/ ERK, p-p38 MAPK/ p38 MAPK and p-JNK/ JNK protein in the walnut green husk extract high concentration + NSC228155 group increased, and the rate of TUNEL positive cells, the apoptosis rate, the expression level of Bax protein decreased, with statistically significant differences (P<0. 05). CONCLUSIONS: Walnut green husk extract may inhibit the proliferation of breast cancer MCF-7 cells and induce the apoptosis by inhibiting the EGFR/ MAPK signaling pathway. [ABSTRACT FROM AUTHOR]