More recently, a new method for ER mature transcript quantification in single cells has been validated in a study by Annaratone L. et al., consisting in a single-molecule RNA fluorescent in Situ Hybridization (FISH) in formalin-fixed, paraffin-embedded tissue sections (FFPE-smFISH), which allows for the quantification and spatial localization of the heterogeneous intratumor ERα expression, thus revealing that its spatial distribution can vary substantially even in the same tumor lesion [83]. The gene discussed is ESR1; the disease is neoplasm.