ESR1 and neoplasm: Possibilities for these cases include: (i) the RNA-seq result was false-negative for the presence of an active ESR1 fusion; (ii) the exome sequencing was a false-negative for the presence of an ESR1 mutation; (iii) the MOTERA score was a false-positive that reflects WT ERα activity because the sample was taken when the patient was not taking ET and the tumor was still E2 dependent; and (iv) some WT ERα MBC persist by expressing a similar MOTERA signature that might be driven by other mechanisms, like TFs other than ERα.