How Are Cancers and Tumors Characterized? Cancer is a collection of diseases characterized by the uncontrolled proliferation of cells. Depending upon the type and purpose of the reporting, a combination of two or more classification and staging approaches is used to identify and describe the type of cancer a person has: BY SITE OF ORIGIN Classifies cancers based on the organ in which cancer originated, e.g., breast cancer, or lung cancer. BY TISSUE TYPE Classifies cancers based on the type of tissue in which cancer originated. Carcinoma Begins in the skin or in tissues that line or cover internal organs. Sarcoma Begins in bone or in the soft tissues of the body, such as fat or muscle. Myeloma Begins in plasma cells, a type of white blood cell. Leukemia Begins in bloodforming tissue, such as the bone marrow. Lymphoma Begins in cells of the immune system. BY GRADE Classifies cancers based on how tumor cells appear when examined under a microscope. If cells look more normal, a tumor might be called well differentiated in the pathology report. If cells look less normal, a tumor might be called poorly differentiated or undifferentiated and is considered more aggressive. GRADE X Undetermined grade When a grade cannot be assessed. GRADE 1 Low grade When cells are well differentiated. GRADE 2 Intermediate grade When cells are moderately differentiated. GRADE 3 High grade When cells are poorly differentiated. GRADE 4 High grade When cells are undifferentiated. BY SPREAD Classifies cancers based on the extent to which cancer has spread in the body. This approach to describe cancer is called the TNM staging system (where T refers to the primary tumor; N refers to the regional lymph node—a tissue in the lymphatic system (see The Lymphatic System, p. 33); and M stands for metastasis—when cancer has spread to parts of the body that are distant from the primary site of origin. In the TNM staging system, clinicians consider the size of the tumor (larger size is typically considered a more aggressive tumor), and whether the cancer has spread from where it started to nearby lymph nodes (higher number of lymph node containing cancer is typically considered a more aggressive cancer), or other parts of the body (metastasis). A simplified description of cancer stages using this approach is described below: Precancerous stage A condition that may become cancer in the future if untreated. Stage I Cancer that is localized to the tissue of origin. Stage II Cancer that has spread to nearby tissues. Stage III Cancer that has spread to nearby lymph nodes or other tissues to a higher extent than Stage II. Stage IV Cancer that has spread to distant lymph nodes or other distant tissues. It is important to note that characterization of cancers, as well as their treatment, increasingly includes biological and molecular properties of cancer, thanks to research-driven knowledge of the genetic and epigenetic makeup of cancer. For example, breast cancer is further characterized by the presence or absence of estrogen, progesterone, and HER2 receptors. Developed from (63). SIDEBAR 5 AACR Cancer Progress Report 2023 Understanding the Path to Cancer Development 26
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