Both cytofluorimetric and immunohistochemistry (IHC) analysis highlighted the presence of a subpopulation expressing the putative BC stem cell immunophenotype (CD44+/high/CD24−/low), responsible for tumor maintenance and relapse [29] (Supplementary Figure S2a–c), suggesting that primary tumor-cell heterogeneity is preserved in organoids. The gene discussed is CD44; the disease is breast cancer.