We identify CTC clusters of small and large size (from two to more than 50 cells) in patients with luminal-A-like (n = 1/8), luminal-B-like (n = 3/13) or HER2-positive (n = 1/3) disease, while no CTC clusters were found in patients with triple-negative breast cancer (n = 0/4). The gene discussed is ERBB2; the disease is triple-negative breast carcinoma.