Human breast cancer cell lines were screened for PI-phosphatase expression via droplet digital PCR and immunoblotting, which revealed the highest co-expression of PIPP and PTEN in T47D, ER+ breast cancer cells, with lower levels in non-transformed MCF-10A, ER + MCF-7, HER2 + SKBR3 and triple negative MDA-MB-231, Hs578T and SUM185PE cells (Supplementary Fig. S2). This evidence concerns the gene ESR1 and breast cancer.