In the living biobank of canine mammary tumor organoids (47), PIK3CA-mutated organoid lines were more sensitive to an inhibitor of the PI3K/AKT pathway, alpelisib and tolerant to an inhibitor of the MDM2-TP53 interaction, nutlin-3a which has effects on other organoid lines, suggestive of a practical tool to investigate whether specific mutations predict therapy outcomes. The gene discussed is PIK3CA; the disease is breast cancer.