The aim of this handbook is to provide information about types of cancer, problems caused by cancer, the possibilities of anti-cancer treatment, complications associated with this treatment and their effects. The main topic of the book Patient's guide to oncology treatment, to which this publication is dedicated, is the problem of nutrition in cancer and during anti-tumor therapy. An insufficient or inappropriate composition of the diet can worsen the general condition of the patient, thereby worsening the course and often the results of the treatment. The tumor itself or anti-tumor treatment can cause food intake disorders or disrupt and change the processes of digestion and metabolism. The Patient's Guide to Oncology Treatment manual is divided into a theoretical part, where you can find general information about cancer, antitumor treatment, and organ symptoms that can be caused by a tumor or antitumor treatment. The second part of the manual is practically focused, here you will find advice on how to behave in the event of problems complicating the intake and processing of food.