ESR1 and breast carcinoma: Accordingly, the 2020 ASCO/CAP update introduced a new reporting category of “ER-low positive” for breast cancers with 1–10% ER positivity, with a comment stating, “there are limited data on the overall benefit of endocrine therapies for patients with low level (1–10%) ER expression, but they currently suggest possible benefit, so patients are considered eligible for endocrine treatment”5.