In U266B1 (multiple myeloma) and βTC (neuroendocrine pancreatic cancer), the cost/benefit ratio of the growth factor that was knocked out (respectively, IL6 and IGF2) was high enough to enable the KO clone to spread in the WT population and induce the collapse of cooperation, at least at high FBS. The gene discussed is IGF2; the disease is pancreatic endocrine carcinoma.