Six tumors from each group were randomly selected based on similar sizes and analyzed as individual tumors (left panel). These six individual tumors from each group were combined as a single pooled sample (right panel). Protein levels of pErbB2, ErbB2, pErbB1, ErbB1, pErbB3 and ErbB3 were determined by Western blot analysis. β-Actin was used as a loading control. For the pooled samples (right panel), quantitation of Western blots was performed by Image J 1.44p (NIH), and the numbers are provided at the bottom of each Western blot.