Since all tumor samples had been laser capture microdissected to minimize the influence of contaminating non-neoplastic cells, we therefore hypothesize that the low-level of ESR1 copy number changes and copy number heterogeneity could have obscured detection of ESR1 amplification by MLPA (e.g. in samples 5, 9 and 26, see Table S1). Here, ESR1 is linked to neoplasm.