What is cancer and how it develops
Cancer (malignant tumor) is a disease that is a consequence of an irreversible change in the cell nucleus, mutation of gene, either in body or germ cells. Changes of genes (gene mutations) can be inherited or they develop during life-time. In some cases, the cancer is caused by an abnormal gene that is being passed along from parents to their children. Although this is often referred to as inherited cancer, what is inherited is the abnormal gene that can lead to cancer, not the cancer itself. Inherited cancer, where the risk of disease is high, is rare in the population and it accounts for less than 5% of all cancers. More important are metabolic changes in cells that are inherited and help to repair the damage in genes, caused by several environmental factors. These risk factors from physical environment (e.g. UV radiation of the sun), chemicals (e.g. tobacco smoke) or biologic agents (e.g. HPV virus) may cause mutations directly or they damage the normal cell repair mechanisms.
Because of irreversible damage to genes, cells in a part of the body start to grow out of control. Cancer cells can also grow into other tissues; they travel along lymph vessels into lymph nodes or spread through the blood to distant organs, and cause distant metastases. Growing out of control and invading other tissues are what makes a cell a cancer cell. The process of initial mutation to the time when a disease can be diagnosed as a lump or change in organ function is long, it takes several years or even decades.
Any cell in the body may turn cancerous. According to the tissue of origin, cancer types can be grouped into four main categories:
· Carcinoma is a cancer that begins in the epithelial cells of skin or in tissues that line or cover internal organs; they present about 80% of all cancers.
· Sarcoma is a cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue.
· Leukemia is a cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced and enter the blood. They usually not present as a lump.
· Lymphoma is cancer of that begins in the cells of lymphatic tissue that is formed from lymphatic vessels and lymph nodes. It works as a filter preventing harmful substances (e.g. infectious agents) entering the blood.
As far as cancer is limited to the epithelium, not spreading to underlying tissues, it is called "intraepithelial" or "in situ" cancer and is not classified as cancerous disease. Such a disease can be cured with a minor surgery. The incidence of this type of breast, cervical and colorectal cancer are of special interest, as they show the effectiveness of screening programmes, especially population based organised programs; in Slovenia these are the programs ZORA, DORA and SVIT. The Cancer Registry of RS is registering intraepithelial breast lesions since 1987 and intraepithelial cervical since 1993; the intraepithelial bladder lesions and melanoma stage Clark I are registered since 1995.
The tissue of basic cancer groups has many special morphologic characteristics. They can be observed by microscope, with additional staining or with other techniques. Pathologists group morphology characteristics in several groups and classify them according to special classifications. These characteristics often influence the course of disease and treatment outcome.
Cancer can arise in nearly every organ. In order to classify cancer according to the site of origin, the International Statistical Classification of Diseases and Related Health Problems (ICD) is used, prepared by World Health Organisation. Every ten years, a revised version is issued, currently the 10th is available. It is used by the Cancer Registry of RS since 1997; before, the 8th revision.
At diagnosis, cancer can be just a small, hardly visible alteration or cancer can spread to adjacent tissues, lymph nodes or to distant organs. The extent of disease doctors classify in several stages according to different systems, most often according to TNM classification. In this classification, the stage is based on the size of the tumor and whether the cancer has spread to lymph nodes or other parts of the body. A simplified definition of stages is generally used for stage classification by registries: localised, regional and remote.
