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Conventional chemotherapeutics and ionizing radiation can promote therapy-induced senescence in tumor cells in vitro as well as in patients, contributing to or being responsible for tumor recurrence. Here we show some common features of Hela and MCF7 senescent cells  induced by chemotherapy or ionizing radiation. 

Common features induced by chemotherapy or ionizing radiation in HeLa and MCF7 cells:

• a dramatic alteration in size revealed by cytoplasm-nucleous ratio (panels A and B), staining of attached cells with crystal violet dye clearly shows cell flattening (observed under phase contrast microscopy, panels C-F);
• an intense ß-gal positivity (observed under phase contrast microscopy, panels G-J);
• an abundance of lipid droplets revealed by Oil Red O staining (observed under phase contrast microscopy, panels K-N);
• a senescence-associated heterochromatin foci (SAHF) as identified by immunofluorescence microscopy upon chromatin staining with DAPI and antibodies that recognize phosphorylated histone 2AX, H2AX (panels O-R);
• a  hypermetabolic status represented by a heightened mTOR staining in immunofluorescence microscopy (S-V).