There is no safe evidence that certain food have any effect on the growth rate of an existing tumor or lead to the formation of tumor cells in the body. However, diet and nutritional status of cancer patients, are important for the course of the disease, since it can not fix the general condition, the strength and confidence of patients and the quality of life. In addition, about 50% of patients with malignant diseases (depending on the type of tumor) appear various problems regarding diet, either as a direct result of the growth of tumors or as side effects of treatment. In addition to problems in the diet which leads to the disease itself, are possible secondary nutritional problems that arise due to the specific nature and localization of the tumor, as well as therapy. An additional problem is to reduce the resistance of the organism, which favors the development of infections, especially opportunistic. The basic diet for patients with malignant diseases should be energetic and biologically appropriate and easily digestible. The energy value of a child is determined individually and depends on the mobility of patients, the appetite and the like. The diet should be made in the entry of fresh foods and fresh squeezed juices. Vegetables and fruits during the thermal preparation should be just a little boiled / grilled. It is recommended to reduce consumption of meat, while fish usage (an excellent source of omega-3 fatty acid) is very recommendable.