Cancer is not a single disease but a collection of over 100 different diseases. These diseases are characterized by the uncontrolled growth and spread of abnormal cells. Understanding “What Is In Cancer” begins with recognizing that cancers are primarily classified based on two key factors: the organ or tissue where the cancer originates, and the type of cell from which it develops. For example, cancer that begins in the lungs is termed lung cancer, while cancer starting in the brain is known as brain cancer. Furthermore, cancers are also categorized by the specific type of cell that gives rise to them, such as epithelial cells or squamous cells.
To explore specific cancer types, resources like the NCI website offer detailed information, categorized by body location and an A to Z list. There are also specific resources for childhood cancers and cancers affecting adolescents and young adults.
Broadly, cancers can be grouped into several major categories based on the type of cells they originate from. Let’s delve into some of these primary categories:
Major Categories of Cancer
Carcinoma
Carcinomas represent the most frequently diagnosed type of cancer. They originate in epithelial cells, which form the lining of organs and cover the surfaces of the body, both internally and externally. Epithelial cells are diverse, often appearing column-shaped under a microscope.
Different types of carcinomas are further classified based on the specific epithelial cell type involved:
- Adenocarcinoma: This type of carcinoma develops in epithelial cells specialized in producing fluids or mucus. These tissues are often referred to as glandular tissues. Common examples include adenocarcinomas of the breast, colon, and prostate.
- Basal Cell Carcinoma: Originating in the basal layer, the deepest layer of the epidermis (outer skin layer), basal cell carcinoma is a common skin cancer.
- Squamous Cell Carcinoma: This carcinoma arises from squamous cells, epithelial cells situated just beneath the skin’s outer surface. Squamous cells also line various organs like the stomach, intestines, lungs, bladder, and kidneys. Under a microscope, these cells appear flat, resembling fish scales. Squamous cell carcinomas are sometimes referred to as epidermoid carcinomas.
- Transitional Cell Carcinoma: This type develops in transitional epithelium, or urothelium, a specialized tissue composed of multiple layers of epithelial cells capable of stretching and shrinking. This tissue lines the bladder, ureters, parts of the kidneys (renal pelvis), and certain other organs. Some bladder, ureter, and kidney cancers are transitional cell carcinomas.
Sarcoma
Sarcomas are cancers that originate in the bone and soft tissues of the body. Soft tissues include a wide range of structures such as muscle, fat, blood vessels, lymph vessels, and fibrous tissues like tendons and ligaments.
- Osteosarcoma is the most prevalent form of bone cancer.
- Soft tissue sarcomas are diverse, with common types including leiomyosarcoma, Kaposi sarcoma, malignant fibrous histiocytoma, liposarcoma, and dermatofibrosarcoma protuberans. Soft tissue sarcoma affects the supporting structures of the body.
More detailed information can be found on resources dedicated to soft tissue sarcoma.
Leukemia
Leukemias are cancers that start in the blood-forming tissue of the bone marrow. Unlike many other cancers, leukemias do not form solid tumors. Instead, they are characterized by an overproduction of abnormal white blood cells (leukemia cells or leukemic blast cells). These abnormal cells accumulate in the blood and bone marrow, crowding out healthy blood cells. This crowding can lead to complications such as reduced oxygen supply to tissues, bleeding issues, and increased susceptibility to infections due to the lack of normal blood cells.
Leukemias are categorized into four common types based on their progression rate (acute or chronic) and the type of blood cell affected (lymphoblastic or myeloid). Acute leukemias progress rapidly, while chronic forms develop more slowly.
Further information can be found on dedicated leukemia resources.
Lymphoma
Lymphoma is a cancer that begins in lymphocytes, a type of white blood cell crucial for the immune system. Lymphocytes include T cells and B cells. In lymphoma, abnormal lymphocytes accumulate in lymph nodes and lymph vessels, as well as other organs throughout the body.
There are two primary types of lymphoma:
- Hodgkin Lymphoma: This type is characterized by the presence of abnormal lymphocytes called Reed-Sternberg cells, which typically originate from B cells.
- Non-Hodgkin Lymphoma: This encompasses a large group of lymphomas that start in lymphocytes. These cancers can grow at varying rates and can develop from either B cells or T cells.
More detailed information is available on resources specializing in lymphoma.
Multiple Myeloma
Multiple myeloma is a cancer that originates in plasma cells, another type of immune cell. In multiple myeloma, abnormal plasma cells, known as myeloma cells, accumulate in the bone marrow and form tumors within bones throughout the body. Multiple myeloma is also referred to as plasma cell myeloma or Kahler disease.
Detailed information can be found on resources dedicated to multiple myeloma and other plasma cell neoplasms.
Melanoma
Melanoma is a cancer that begins in melanocytes, specialized cells that produce melanin, the pigment responsible for skin color. While most melanomas develop on the skin, they can also occur in other pigmented tissues, such as the eye.
More information is available on resources about skin cancer and intraocular melanoma.
Brain and Spinal Cord Tumors
Brain and spinal cord tumors are diverse, categorized by the cell type of origin and the tumor’s initial location within the central nervous system. For instance, an astrocytic tumor originates in astrocytes, star-shaped brain cells that support nerve cell health. Brain tumors can be benign (non-cancerous) or malignant (cancerous).
Further information is available on resources about brain and spinal cord tumors.
Other Types of Tumors
Germ Cell Tumors
Germ cell tumors develop from cells that give rise to sperm or eggs. These tumors can occur in various body locations and can be either benign or malignant.
Resources categorized by body location include a list of germ cell tumors with links to further information.
Neuroendocrine Tumors
Neuroendocrine tumors arise from cells that release hormones into the bloodstream in response to nervous system signals. These tumors may produce excessive hormones, leading to various symptoms. Neuroendocrine tumors can be benign or malignant.
Definitions and more information on neuroendocrine tumors are readily available.
Carcinoid Tumors
Carcinoid tumors are a subtype of neuroendocrine tumor. They are slow-growing and typically found in the gastrointestinal system, most commonly in the rectum and small intestine. Carcinoid tumors may spread to the liver or other body sites and can secrete substances like serotonin or prostaglandins, causing carcinoid syndrome.
Resources on gastrointestinal neuroendocrine tumors offer more detailed information.
In conclusion, understanding “what is in cancer” involves recognizing the vast diversity of cancer types. Each type is defined by its cellular origin and location, influencing its behavior and treatment approaches. This overview provides a foundational understanding of the major categories of cancer, highlighting the complexity of these diseases and the importance of specific diagnoses for effective management.
