Breast cancer with neuroendocrine differentiation detected by unique staining pattern of neoplastic cells in hercep test.

Hercep Test (DAKO) is an immunohistological screening kit to select cases of advanced breast cancer with indication for treatment with a humanized mouse monoclonal antibody to human epidermal growth factor receptor-2, trasthzumab (Herceptin). We report a case of an 84-year-old female with invasive ductal carcinoma of the right breast, whose neoplastic cells showed a unique staining pattern in Hercep Test. The cells showed an intracytoplasmic fine granular staining pattern, instead of the membranous pattern of typical breast cancer cells.