What food is good to build up immune system for cancer patient who is undergoing chemotherapy?

Healthy diet: In general probably foods high in good healthy nutrients like lots of veggies, berries and fruit. However, you may want to ask your oncologist to refer you to a dietician to evaluate your current diet and make further recommendations. Food with high levels of antioxidants may help also. Probably a good balance of lean protein if you are losing weight will help also.

Diet and chemo: There is no "special immune building" diet recommended for patients undergoing chemotherapy. In general a balanced diet with enough proteins and fruits/ vegetables is preferable. Chemo can suppress appetite but it is very important to maintain your weight while going through these therapies.