PurposeTo determine whether (1) immunohistochemical (IHC) HER2 status (ie, 2+ or 3+), (2) degree of fluorescence in situ hybridization (FISH) amplification according to (2a) HER2/CEP17 ratio or (2b) HER2 gene copy number, or (3) polysomy significantly influenced clinical outcome for patients with human epidermal growth factor receptor 2 (HER2) –positive breast cancer enrolled in the Herceptin Adjuvant trial of trastuzumab versus no trastuzumab administered after completion of chemotherapy.Patients and MethodsIHC and/or FISH analyses were performed locally and required central confirmation as indicating HER2 positivity for trial entry. FISH data from the central HER2 analysis on patients in the 1-year trastuzumab and no trastuzumab arms were assessed in relation to disease-free survival (DFS) after a median 2 years of follow-up.ResultsCentral FISH results were available for 2,071 (61%) of the 3,401 patients randomized to the 2 arms. Among patients with FISH-positive disease, (1) the hazard ratios for trastuzumab versus no trastuzumab were 0.56 (95% CI, 0.32 to 0.99) for locally IHC2+ cases (n = 340) and 0.80 (95% CI, 0.40 to 1.61) for centrally IHC2+ cases (n = 299). There was no significant prognostic relationship between (2a) HER2 FISH ratio, (2b) HER2 copy number, or (3) polysomy and DFS in the control arm or predictive relationship defining differential benefit from trastuzumab.ConclusionThere was no evidence for reduced benefit of trastuzumab in HER2 IHC2+FISH+ cases. The degree of HER2 amplification does not influence prognosis or benefit from adjuvant trastuzumab in patients treated with prior adjuvant chemotherapy.

Extracellular signal regulated kinase 5 (ERK5) is a novel member of the mitogen-activated protein kinase (MAPK) family with a poorly defined physiological function. Since ERK5 and its upstream activator MEK5 are abundant in skeletal muscle we examined a function of the cascade during muscle differentiation. We show that ERK5 is activated upon induction of differentiation in mouse myoblasts and that selective activation of the pathway results in promoter activation of differentiation-specific genes. Moreover, myogenic differentiation is completely blocked when ERK5 expression is inhibited by antisense RNA. Thus, we conclude that the MEK5/ERK5 MAP kinase cascade is critical for early steps of muscle cell differentiation.