ERBB2 and cancer: Consequently, the expression of t-erbB2 proteins (p95, p110, or Δ16) in cancer cells suggests one possible resistance mechanism against antibody-based anti-HER2 therapies.1,7 Some, though not all,11 clinical studies have shown that metastatic HER2-positive patients expressing t-erbB2s have worse clinical outcomes when treated with trastuzumab,12 as evidenced by shorter progression-free survival rates.13,14 Comparison was made to patients expressing only full-length HER2.