Is it permissible for a cancer patient, who has undergone surgeries and been weakened by them, to break his fast in Ramadan and make up the days he missed on other short days when he is able to fast?

A sick person is permitted to break their fast if fasting harms them or delays their recovery. Indeed, breaking the fast becomes obligatory if there is a fear of perishing or suffering severe harm. If they are able to make up the missed fasts (qada'), they should do so. Otherwise, according to the majority of scholars, the obligation to fast is waived, and expiation (fidyah) becomes due, which is one mudd (a measure of food) for each day. As for someone who is able to fast but their work is strenuous, they must fast and take measures to facilitate fasting, such as reducing or leaving their work. They are not permitted to break their fast on the grounds of strenuous work.