What is childhood cancer?

Author:  Gesche Tallen, MD, PhD, Editor:  Maria Yiallouros, Reviewer:  Prof. Dr. med. Dr. h. c. Günter Henze, English Translation:  Hannah McRae, Last modification: 2012/04/25 https://kinderkrebsinfo.de/doi/e1820

Cancer describes a series of diseases which have in common the uncontrolled growth of cells, which can invade healthy parts of the body. Normal cells have inner clocks that regulate the different phases of life. These inner clocks, in cooperation with signals from other cells, tell a cell when and how to divide, grow, mature, age, and die. Cancer cells lack these regulatory clocks and are thus referred to as "immortal" because they cannot stop growing on their own.

Cancer in people younger than 20 years is rare in Europe, as it accounts for only 1% of all childhood diseases.
Theoretically, every cell in the human body can turn into a cancer cell. Therefore, there are many different types of cancer in children, teenagers, and adults. Cancer can cause different symptoms because it can originate anywhere in the body and affect any number of organs and tissues. Therefore, each type of cancer requires a specific treatment and has a different outcome.

Cancer can occur as a leukaemia or as a lymphoma, thereby affecting the complete blood forming or lymphatic system. The ability to affect many organs of the human body makes cancer, professionally speaking, a systemic disease. Cancer cells often build clusters (solid tumours) in organs and are named based on the tissue of origin. For example, if having arised from nerve cells, connective or supportive tissue, such as cartilage, bone, or muscle, a tumour is called a sarkoma. Carcinomas develop from changes in cells of glands or organ walls. Carcinomas are rather rare in children. If a tumour originates from very primitive cells (embryonal cells or blasts), which is very typical for tumours in children and teenagers, its corresponding name usually ends with -"blastoma". It is often difficult to determine the cell or tissue type of origin in a blastoma, due to the primitivity and immaturity of its cells.

Cancer cells are typically out of control and divide without a limit. While they are dividing, they often copy their malignant characteristics. Most of the time, they do not function properly. Instead, they can spread wihtin the region where they arose (locally) and travel to sites of the body that are far away from their origin (metastasis). It is assumed that, although often not detectable by routine tests, every cancer has already produced numerous tiny (micro-) metastases by the time of initial diagnosis. The ability to spread makes cancer a malignant disease, meaning that, if not treated appropriately, it can progress and lead to death.

Therefore, treating the visible malignant tumour alone is not enough. Instead, even the tiniest spread (micrometastases) has to be considered and treated from the start. This approach is called systemic treatment. In fact, no matter which cell type the cancer has arisen from, the disease almost always affects the whole body.

Cancer's numerous aggressive properties make it a malignant, and even--if not treated--a fatal disease.