PIN1 and breast cancer: To better understand whether PIN1 levels were not only associated with poor prognosis but also developed with treatment resistance, we performed multiplex immunohistochemistry (mIHC) assays to comprehensively examine the protein levels of PIN1 at the single-cell resolution in paired breast cancer tissue specimens collected from 9 patients before treatment with the combination of an estrogen receptor blocker and the CDK4/6-inhibitor Palbociclib, as well as after disease progression on the treatment and subsequent discontinuation of the treatment (Supplementary Fig. 1b, Supplementary Table 2).