If participants really have a lack of AA after chemotherapy, AA supplementation could be beneficial for the immune recovery in many future patients on chemotherapy. However, the participants cannot benefit yet, because this study does not interfere with current clinical practice. The risks associated with participation in this study are low. Venous blood sampling is performed by skilled and experienced laboratory technicians. For the study, only a small amount of blood, 5 to 7 times 17 ml is needed. Therefore no harm can be expected. Blood withdrawal could result in a hematoma, but this is usually not harmful. Bleedings from the blood withdrawal are usually negligible.