Human epidermal growth factor receptor 2 amplification as a biomarker for treatment in patients with lymph node-metastatic penoscrotal extramammary Paget's disease

The role of human epidermal growth factor receptor 2 (HER2) amplification as a biomarker for treatment in patients with lymph node (LN)-metastatic penoscrotal extramammary Paget's disease (EMPD) was investigated in the present study. A total of 11 male patients with LN-metastatic penoscrotal EMPD were retrospectively reviewed. Positron emission tomography/computed tomography (PET/CT) was conducted prior to surgery. Immunohistochemistry and fluorescence in situ hybridization were used to evaluate HER2 gene amplification in LN samples. Sanger sequencing was used to investigate HER2 mutations. A literature review of the prevalence of HER2 amplification in EMPD and the efficacy of HER2-targeted therapy was also undertaken. PET/CT is effective in detecting metastatic sites. The sensitivity and specificity of PET/CT was 90.9 and 100.0% for inguinal LNs, and 85.7 and 80.0% for pelvic LNs, respectively. The median time from LN dissection to disease progression was 15.9±1.5 months. Of the 11 patients, 3 (27.3%) indicated HER2 amplification. Patients with HER2 amplification showed shorter median times from disease discovery to LN metastasis (HER2 amplification vs HER2 non-amplification; 15.6 vs. 10.0 months; P=0.50) and from LN dissection to disease progression (HER2 amplification vs. HER2 non-amplification, 16.2 vs. 13.6 months; P=0.11). However, the aforementioned observations were not indicated to be statistically significant. No HER2 mutations were identified. Trastuzumab, a HER2-targeted monoclonal antibody, was administered to 2 of the patients with HER2 amplification. A literature review of the prevalence of HER2 amplification in EMPD and the efficacy of HER2-targeted therapy showed similar results. Altogether, 485 cases of EMPD were reported, 35 of which had metastases. The results in the present study suggest that PET/CT should be used on all metastatic EMPD patients. EMPD may be effectively treated with trastuzumab. The present study and case reports from the literature provide evidence for the benefit of testing for HER2 amplification in this rare disease and highlight the requirement for a multicenter clinical trial to assess the impact of trastuzumab therapy in treating this disease.