Differential induction of apoptosis in doxorubicin-treated organotypic breast tumors. (A) Breast tumors (n = 33) were incubated with 10 μM doxorubicin (Doxo) for the indicated time intervals and analyzed for cleaved caspase-3 (Casp3), by immunohistochemistry. (B) Responder (n = 19) versus Non Responder (n = 14) breast tumors were analyzed for Casp3 expression after 72 h treatment with vehicle (Ctrl) or Doxo by immunohistochemistry. Original magnification x 400. (C) Quantification of Casp3 immunoreactivity in Non Responder versus Responder breast tumors at the indicated time intervals after Doxo treatment. #P = 0.04; *P = 0.02. (D) Quantification of growth index (GI) in Responder versus Non Responder breast tumors at the indicated time intervals after Doxo treatment. *P = 0.02; ***P = 0.0005 (unpaired t test). Each circle corresponds to an individual tumor. (E) γH2AX-reactive cells were quantified after 48 h treatment with Doxo in Responder or Non Responder breast tumors by fluorescence microscopy. For all experiments, bars represent mean ± SEM.