The impact of genetic mutations, growth factor stimulation, gene silencing/overexpression or drug administration can be objectively quantified ex vivo: by counting the numbers of duct-like structures or quantifying the expression of ductal-specific markers (e.g., Cytokeratin-19, KRT19) after a few days in culture, investigators evaluate the propensity of acini to undergo ADM, which correlates with tumor initiation capacity. The gene discussed is KRT19; the disease is neoplasm.