ERBB2 and cancer: While HR+/HER2-positive tumors clinically respond at least as well to NET as HR+/HER2- tumors in terms of volumetric reduction33,34, data from two clinical trials of standard NET of 4–6 month duration showed that cancer cell proliferation rates (Ki-67-positivity) after NET remained significantly higher in ER+/HER2-positive tumors35.