Phenethyl isothiocyanate (PEITC) suppresses the growth of MDA-MB-231 (high HER2 (HH)) tumors by inhibiting HER2 in SCID/NOD mice. About 5 × 106 MDA-MB-231 (HH) cells were subcutaneously implanted into the right flanks of SCID/NOD mice. Once each mouse had a tumor of about 150 mm3, mice started receiving 12 μmol of PEITC by oral gavage every day. Tumors were measured three times a week, and each mouse was weighed twice a week. Effect of PEITC on (A) tumor volume, (B) tumor weight, (C) Mice weight and (D) tumor western blots. Tumors were minced, lysed and analyzed for HER2, epidermal growth factor receptor (EGFR), phosphorylated signal transducer and activator of transcription 3 (p-STAT3) (Y-705), STAT3 expression, BIM, B-cell lymphoma-extra large (BCL-XL), X-linked inhibitor of apoptosis protein (XIAP), cleaved poly-ADP ribose polymerase (PARP) and cleaved caspase 3. Blots were stripped and reprobed with actin antibody to verify equal protein loading. Each lane represents a tumor sample from different mice. The blots were quantitated, normalized with actin and represented as bars.