To test whether this was due to the development of resistance to the TNF/Mel/SM treatment or was caused by attaining a transient state called “persistence” without mutation (Hangauer et al, 2017; Viswanathan et al, 2017), we isolated drug‐tolerant tumour cells from three rats (124, 133 and 136) that developed sarcomas post‐treatment. The gene discussed is TNF; the disease is sarcoma.