Cancer is not a single disease but rather a few hundreds of different diseases that can develop in any tissue or organ of the human body. In medical terminology, terms such as neoplasm, malignancy, or malignant tumour are also used.

The fundamental characteristic of cancer is the uncontrolled growth and division of altered cells, which can spread to neighbouring tissues or other parts of the body. The formation of a cancer cell is a complex process called carcinogenesis. Several years or even decades may pass from the initial cellular change until the disease becomes detectable, either as a lump or as a change in organ function.

There are many different types of cancer. The basic classification is based on the organ or tissue where it originates (e.g., breast cancer, lung cancer, bone cancer), while a more precise definition is possible through microscopic examination of tumour tissue and additional pathological and molecular tests.

Individual types of cancer differ in prevalence, disease progression, treatment methods, and prognosis. They also have various risk factors, some better known than others. Among the most important are those related to lifestyle, which individuals can influence to a large extent, although they are also affected by broader social and environmental conditions as well as the availability of public health measures. It is estimated that between 30 and 50 percent of all cancers could be prevented, as they are linked to risk factors such as smoking, alcohol consumption, poor diet, insufficient physical activity, and excessive exposure to UV radiation. Survival for cancer patients are primarily influenced by age and the stage of the disease at diagnosis.

The main reason for the rising number of cancer patients is the aging population. With few exceptions, cancer is a disease of the elderly; therefore, as the proportion of older adults in the population increases, so does the number of new cases. Other contributing factors include increased life expectancy, lifestyle changes, and social and environmental factors. Through the national cancer screening programs ZORA, DORA, and Svit, significant progress has been made in reducing the burden of cervical, breast, and colorectal cancer.

Cancer remains a major public health challenge, so monitoring its burden and trends is crucial for planning effective measures for prevention, treatment, and patient support.