H2AX and breast cancer: Double immunofluorescence was performed in widely different cell lines, including H9C2 cardiomyocytes, MCF-7 and T47D human breast cancer cells, and BxPC-3 and PANC-1 pancreatic cancer cells to correlate BRCA1 subcellular localization with IR-induced γ-H2AX foci, a marker of double strand DNA breaks and nuclear localization, 1 hour after 5 Gy ionizing radiation.