Refinement of the flow cytometric analysis for a routine use in future prospective clinical trials will help to evaluate the value of determining both the numbers of HER2+EVs and their HER2 expression levels and will demonstrate whether it can provide relevant information on the HER2 status in breast cancer patients in situations where a biopsy may not provide sufficient information, such as in multifocal tumours that may present with different immunohistochemical profiles [7, 40, 41] or in patients with breast cancer metastasis. The gene discussed is ERBB2; the disease is breast cancer.