We are at the early stages of understanding the disease process of cancer. It is difficult to make decisions when it comes to treating affected animals. Subjecting animals to anaesthetics and toxic drugs to achieve remission is a moral dilemma. Homeopathy is not the magic bullet for treating cancer and does not claim to be so. However, the clinical experience that Sue Armstrong has gained over thirty years of treating veterinary cancer patients that could not tolerate chemo- or radiotherapy, or whose owners could not afford to treat using these methods or refused to treat conventionally, has given her insights not only into a methodology for treating cancer cases but also into the disease process itself. In the first volume of the series, the expert vet describes the scope of homeopathy. She looks at the basics of how cancer arises, its genetic origins and the role of inflammatory processes and oxygen. Then she describes the development of homeopathic cancer treatment from Hahnemann until today, showing the successful approaches of famous homeopaths such as Kent, Grimmer, Ramakrishnan, and Burnett. Sue Armstrong describes her approach in great detail, distinguishing the various stages of cancer. In animals with a strong predisposition for cancer, a great deal can be achieved by prophylactically altering the diet and using miasmatic treatment. If the tumour is confirmed, treatment is selected according to the stage of the cancer and, for example, whether surgery is indicated. Organotropic remedies, drainage and Schuessler salts are used supportively together with the major cancer nosodes Carcinosinum and Scirrhinum. Clear instructions are also provided for treating the effects of cancer such as cachexia, disturbances in haemoptysis or vomiting. She documents her approach with impressive cases. At the end there is a concise materia medica of cancer remedies.