Culturing of the tumor tissue slices under control conditions only marginally affected tissue integrity and viability or not at all, as indicated by marginal differences in immunohistochemical localization of fragmented cytokeratin (indicative of cancer cell debris), apoptotic cells (c‐CASP‐3), and proliferating cells (PCNA) compared to directly fixed tissue (scoring method in Fig. S4 and results in Fig. S5). The gene discussed is PCNA; the disease is cancer.