Welcome to Healthcare-Magic
Thanks for the query.
It is always hard to predict the dynamics of tumor
spreading,especially metastatic but it will cause by statistics faster spreading and less life expectancy. However many people quit chemoth since generally this life prolongation with chemoth is usually just few or several months and chemo effects may be unbearable. So it is his decision and whatever he decide it wont be wrong. if he survived 6 months then it may indciate that he has good immune system,but as you already know prognosis is not good.
Wish you good health.