Furthermore, the BrdU assay performed on primary PyMT tumor cells revealed a significant decrease in the proliferation index of PyMT;CstC-/- tumor cells (approximately 30 %) compared to PyMT;CstC+/+ tumor cells (Figure 3E), thereby confirming the Ki67 proliferation data obtained from the analysis of the primary tumor tissues. The gene discussed is MKI67; the disease is neoplasm.