Absence of HER2 overexpression in metastatic malignant melanoma

Background and objectives: Currently available systemic therapies for malignant melanoma produce low response rates in patients, and more effective treatment modalities are clearly needed. Trastuzumab (Herceptin), the antibody to the HER2 oncoprotein, has had a significant impact on therapy for patients with HER2-overexpressing metastatic breast cancer. This study examined the incidences of HER2 protein overexpression and HER2 gene amplification in metastatic malignant melanoma, which remain unclear in the literature.

Methods: The study evaluated patients with stage III and stage IV malignant melanoma who were treated between 1983 and 1999. Tissue blocks were retrieved and reviewed to confirm the diagnosis. From the 101 cases identified, 49 (31 stage III and 18 stage IV) had sufficient residual tumor sample to enable an assay to be performed. The blocks were tested for HER2 overexpression using the DAKO HercepTest immunohistochemical (IHC) assay. Any sample that tested 1+ or greater for HER2 expression on IHC and a randomly selected subset of HER2-negative samples were tested for the presence of HER2 gene amplification using the Vysis PathVysion fluorescence in situ hybridization (FISH) assay.

Results: The median age of the 49 selected patients was 52.2 years, and the male-to-female ratio was 1.23:1 (27 men to 22 women). All of the 49 cases of malignant melanoma were negative for HER2 overexpression by IHC. However, two samples (3%) were found to have a weak level of HER2 expression (1+ level of staining). Subsequent FISH results on the samples that were 1+ on IHC were negative for HER2 gene amplification. FISH results on 21 other randomly selected IHC-negative samples were also negative for HER2 amplification. Flow cytometry failed to show HER2 overexpression in two melanoma cell lines, and treatment of these cells with trastuzumab did not affect their proliferation rate.

Conclusions: We found a low incidence of HER2 expression and no evidence of HER2 protein overexpression or HER2 gene amplification in metastatic malignant melanoma tissues. Therefore, routine testing for HER2 overexpression or HER2 amplification would not be of benefit in this patient population. These results also imply that anti-HER2 therapy with trastuzumab is highly unlikely to provide benefit for patients with metastatic melanoma.