Cancer isn’t a single disease. It’s a group of more than 100 different conditions, all sharing one trait: cells growing out of control. The way doctors classify cancers starts with the type of tissue where the cancer originates, and that distinction shapes everything from symptoms to treatment to prognosis. There are six major categories worth understanding.
Carcinomas: The Most Common Category
Carcinomas account for 80 to 90 percent of all cancer cases. They start in epithelial tissue, which is the cell layer that lines your skin, organs, and internal passageways like the lungs, colon, and bladder. Because epithelial tissue covers so much of the body, carcinomas can appear in a wide range of locations.
Within this broad category, the subtypes reflect which kind of epithelial cell turned cancerous:
- Adenocarcinoma starts in gland cells that produce fluids or mucus. Most breast, colon, prostate, and lung cancers are adenocarcinomas.
- Squamous cell carcinoma starts in the thin, flat cells that form the outer surface of skin and line organs like the esophagus, lungs, and cervix.
- Basal cell carcinoma starts in the round cells sitting just beneath the squamous layer of skin. Basal and squamous cell carcinomas together are the two most common skin cancers.
- Transitional cell carcinoma starts in the stretchy tissue lining the bladder, ureters, and parts of the kidney.
Because carcinomas dominate cancer statistics, many of the cancers people hear about most often, including lung, breast, colorectal, and prostate cancer, fall into this group.
Sarcomas: Cancers of Bone and Soft Tissue
Sarcomas start in connective and supportive tissues: bone, cartilage, fat, muscle, tendons, and blood vessels. They’re far less common than carcinomas, making up roughly 1 percent of adult cancers, though they appear more frequently in children and young adults.
The two broad divisions are bone sarcomas and soft tissue sarcomas. Bone sarcomas include osteosarcoma (starting in bone cells) and chondrosarcoma (starting in cartilage). Soft tissue sarcomas are named for the tissue they grow in. Liposarcoma forms in fatty tissue, fibrosarcoma in connective tissue, and leiomyosarcoma in smooth muscle. Memorial Sloan Kettering identifies more than 50 distinct subtypes of soft tissue sarcoma alone, which is one reason these cancers can be difficult to diagnose quickly.
Leukemia: Cancer in the Blood
Leukemia starts in the bone marrow, where blood cells are produced. Instead of maturing normally, white blood cells multiply rapidly and crowd out healthy cells. The name literally means “white blood” in Greek, reflecting the overproduction of abnormal white blood cells that defines the disease.
Leukemias are grouped by how fast they progress and which cell line is affected. Acute leukemias grow quickly and require urgent treatment. Chronic leukemias develop more slowly, sometimes over years, and may not cause symptoms right away. Within each speed category, the cancer is further classified by whether it affects myeloid cells (which normally become red blood cells, platelets, or certain white blood cells) or lymphoid cells (which normally become infection-fighting lymphocytes). That gives four main types: acute myeloid, acute lymphoblastic, chronic myeloid, and chronic lymphocytic.
Outcomes vary enormously depending on the subtype and a person’s age. Acute myeloid leukemia, for example, has a five-year survival rate of about 33 percent overall, but that drops to around 21 percent for people diagnosed between ages 65 and 74, according to SEER data from 2016 to 2022. Childhood acute lymphoblastic leukemia, by contrast, has five-year survival rates above 90 percent.
Lymphoma: Cancer of the Lymphatic System
Lymphoma develops in the lymphatic system, the network of nodes, vessels, and organs (including the spleen, tonsils, and thymus) that filters bodily fluids and produces white blood cells called lymphocytes. When lymphocytes become cancerous, they can accumulate in lymph nodes, causing swelling, or spread to other organs.
The two main branches are Hodgkin lymphoma and non-Hodgkin lymphoma. Hodgkin lymphoma is identified by the presence of a specific abnormal cell visible under a microscope. It tends to follow a more predictable pattern of spread and is highly treatable, with five-year survival rates above 85 percent for most stages. Non-Hodgkin lymphoma is a much larger and more varied group, encompassing more than 60 subtypes that range from very slow-growing (indolent) to highly aggressive. Because the lymphatic system runs throughout the body, lymphoma can potentially appear almost anywhere.
Myeloma: Cancer of Plasma Cells
Myeloma, most commonly called multiple myeloma, starts in plasma cells. These are specialized white blood cells that live in the bone marrow and produce antibodies to fight infection. When plasma cells become cancerous, they multiply in the bone marrow and produce abnormal proteins instead of functional antibodies.
The buildup of these cancerous plasma cells can weaken bones, leading to fractures and bone pain, which is often the first symptom. It can also interfere with kidney function and lower the body’s ability to fight infection. The term “multiple” refers to the fact that the cancer typically affects several areas of bone marrow throughout the body rather than forming a single tumor.
Brain and Spinal Cord Tumors
Cancers of the central nervous system don’t fit neatly into the carcinoma or sarcoma categories because they arise from unique cell types found only in the brain and spinal cord. They’re classified by the specific cell of origin, how the cells look under a microscope (graded 1 through 4), and increasingly by the genetic mutations present in the tumor cells.
Gliomas are the largest group, accounting for about 3 out of every 10 brain tumors. They start in glial cells, the support cells of the brain, and include astrocytomas, oligodendrogliomas, and ependymomas. Glioblastoma, a grade 4 astrocytoma, is the most common malignant brain tumor in adults and one of the most aggressive. It makes up more than half of all gliomas.
A separate class called embryonal tumors, including medulloblastoma, starts from early nerve cells. These are fast-growing, grade 4 tumors that appear most often in children and can spread through the fluid surrounding the brain and spinal cord. Tumor location also matters, because where a brain tumor sits determines both its symptoms and which treatments are feasible.
Germ Cell Tumors and Mixed Types
Some cancers don’t originate in a single tissue type or arise in cells that don’t belong to any of the categories above. Germ cell tumors start in the cells that would normally develop into sperm or eggs. They most often appear in the ovaries or testicles, but can also form in the chest, abdomen, or brain when germ cells end up in the wrong location during fetal development.
Mixed-type cancers contain more than one kind of cancer cell within the same tumor. A mixed germ cell tumor, for instance, can include several distinct subtypes such as teratoma, yolk sac tumor, and embryonal carcinoma all in one mass. Carcinosarcomas are another example, containing both carcinoma and sarcoma components. These mixed tumors are rare, but they’re important because treatment needs to address all the cell types present.
Why Classification Matters
Two cancers in the same organ can behave completely differently depending on their cell of origin. A lung adenocarcinoma and a lung squamous cell carcinoma are both “lung cancer,” but they respond to different treatments and carry different outlooks. Knowing the tissue type, the grade (how aggressive the cells look), and increasingly the specific genetic mutations driving the cancer is what allows doctors to choose targeted therapies rather than relying on a one-size-fits-all approach.
This is also why a biopsy, where a small sample of tissue is examined under a microscope and tested for genetic changes, is a necessary step before treatment begins. The organ where cancer is found tells you the location. The cell type tells you what you’re actually dealing with.