The significance of highlighting the oestrogen receptor low category in breast cancer

Abstract

The latest ASCO/CAP guideline has recommended to report oestrogen receptor (ER) low cases (ER^lo; 1-10%) as "ER low positive category", prompting us to compare the clinicopathologic features, biomarkers, survival and treatment of the ER^lo cases with other subgroups (ER negative (ER^neg) and ER high (ER^hi)). ER^lo cases revealed more similar clinicopathologic and biomarker profiles (including younger age, larger tumour, high proliferation, HER2 and basal markers expression) to ER^neg than ER^hi cancers. The ER^lo cases receiving hormonal therapy showed a similarly poor outcome as ER^neg cancers. However, majority of ER^lo cases were downstaged to stage I in the 8th AJCC pathological prognostic staging, highlighting a risk of potential under treatment. Overall, our data highlighted the differences of ER^lo from other ER^pos cases and their management should be considered separately.