The appearance of pod structures composed of epithelial cells showing colocalization of both Krt5 and Scgb3a2 immunofluorescence is consistent with earlier data showing BC > IS re-differentiation, and supports the notion that residual Krt5-immunoreactivity, in light of the long half-life of intermediate filament proteins36, reflects the BC origin of differentiating IS cells. This evidence concerns the gene KRT5 and breast cancer.