What are the Different Types of Cancer?

"Cancer" is not one disease, but rather a term for over 100 different diseases, all of which have their own biology, risk factors, treatment, and prognosis.

A skin cancer and a leukemia share almost nothing in common clinically: different cells of origin, different growth patterns, different treatments, yet both fall under the same broad label. Understanding how cancer is classified and what distinguishes the major categories makes it far easier to interpret a diagnosis, a headline, or a screening recommendation. This blog will tell you about the classification of cancers, major types, and all of those cancers that account for the majority of diagnoses.

How Cancer Is Classified

Cancers are mainly categorized according to where the cancer cells initially originate — rather than where they may have moved to later in the disease progression. It is worth noting that cancer cells that start in one part of the body and then move to other parts still maintain the properties of their tissue of origin.

The broad groups into which cancers are categorized include:

Carcinomas: Cancers originating from epithelial cells (tissues that cover organs and skin)
Sarcomas: Cancers originating from connective tissue (bones, muscles, fats, cartilage, or blood vessels)
Leukemias: Cancers originating from tissues responsible for blood formation (generally bone marrow)
Lymphomas: Cancers originating from lymphatic or immune system cells
Myelomas: Cancers originating from plasma cells within bone marrow
Central nervous system cancers: Cancers originating from brain or spinal cord tissue.

Each of the broad classifications above includes various forms of cancers based on their organs or cell types of origin such as adenocarcinoma in the case of carcinoma cancers.

Carcinomas: The Most Common Cancer Category

Carcinomas constitute the overwhelming majority of cancer cases because they originate from epithelial cells, which form the lining of skin and most organs. The main types are:

Breast Cancer

It is the most common cancer among Americans, regardless of gender, being located in breast tissues, specifically ducts (ductal carcinoma) and lobules (lobular carcinoma). It is a disease that affects both women and men, although it is about 100 times more common in females. Some risk factors are age, family history, mutations in BRCA1/BRCA2 genes, and hormones.

Lung Cancer

There are two major kinds of lung cancer: non-small cell lung cancer (NSCLC) constitutes around 80-85% of cases, while the other is small cell lung cancer (SCLC). Lung cancer is responsible for most cancer deaths in the U.S., largely caused by smoking but sometimes developing in people who never smoked.

Colorectal Cancer

Colorectal cancer arises either in the colon or the rectum, usually arising from a benign polyp that may eventually turn malignant – the very reason why colonoscopy screening is effective in preventing the disease by simply eliminating polyps at an early stage. There has been an increase in incidences among younger individuals, aged below 50, which led to the reduction of the age at which screenings are recommended to 45.

Prostate Cancer

Prostate cancer is the most common form of cancer among males. Slow growing nature is a feature of prostate cancer that has led to active surveillance being the best option for men who have prostate cancer, while others undergo surgery, radiation, and hormones therapy.

Skin Cancer

Basal cell carcinoma and squamous cell carcinoma, both of which are treatable and seldom deadly, make up the majority of skin cancers. However, the deadliest form of skin cancer, melanoma, is the cause of most fatalities from skin cancer even though it is the least common form of skin cancer. UV rays are the main culprit behind these three types of cancer.

Other Common Carcinomas

Bladder cancer – strongly linked to smoking
Kidney (renal cell) cancer
Pancreatic cancer – notably aggressive, with one of the lowest five-year survival rates of any major cancer, often because it's diagnosed late
Liver cancer – frequently linked to chronic hepatitis B or C infection or cirrhosis
Endometrial (uterine) cancer – the most common cancer of the female reproductive system
Thyroid cancer – generally has a strong prognosis compared to most other cancers.

Sarcomas: Cancers of Connective Tissue

The incidence rate of sarcomas is quite low compared to carcinomas, which only constitute 1 percent of adult cancers. However, their importance lies in the fact that they originate from tissue not commonly associated with cancer development such as bones, muscles, fats, cartilages, tendons, and blood vessels.

Osteosarcoma: Bone Cancer (common in children and adolescents)
Liposarcoma: develops in fatty tissues
Leiomyosarcoma: originates in smooth muscles
Angiosarcoma: arises in blood vessel or lymphatic vessels
Ewing Sarcoma: originates in bones and soft tissues of children and adolescents.

Due to their rarity and diversity, they are usually treated in specialized cancer treatment centers specializing in these particular tumors.

Leukemias: Cancers of the Blood

Leukemia starts from blood-forming tissue, usually bone marrow, and leads to an increased production of white blood cells that are abnormal and prevent normal blood cells from performing their functions. In contrast to solid tumors, leukemia does not create a mass but exists in the form of cells circulating in the bloodstream and in bone marrow.

Leukemias are divided into types according to their development speed and type of blood cells:

Acute lymphoblastic leukemia (ALL) – most common form of leukemia among children
Acute myeloid leukemia (AML) – more prevalent among adults, fast-developing type
Chronic lymphocytic leukemia (CLL) – slow-developing, common form of leukemia among elderly people
Chronic myeloid leukemia (CML) – slowly developing leukemia, associated with a certain genetic mutation called Philadelphia chromosome.

Chemotherapy, target therapy, and, sometimes, stem cell/bone marrow transplantation are used for the treatment of leukemia.

Lymphomas: Cancers of the Immune System

Lymphoma occurs in lymphocytes, the body’s white blood cells which play an important role in the body’s immune system, usually showing up as enlargement of the lymph nodes. There are two types of lymphomas:

Hodgkin Lymphoma

This type of cancer is distinguished by the occurrence of an abnormal cell known as the Reed-Sternberg cell. Although it is fairly uncommon, it is one of the most curable types of cancers.

Non-Hodgkin Lymphoma

There are many more types of Non-Hodgkin Lymphoma, with numerous subcategories which differ greatly in severity, ranging from slowly growing tumors, which may be watched and left alone, to quickly growing ones.

Myeloma: Cancer of Plasma Cells

Multiple myeloma affects plasma cells, a type of white blood cells responsible for antibody formation. Cancerous plasma cells cluster within the bone marrow and displace normal blood cells and may damage bone, resulting in fractures and bone pain. Multiple myeloma is not common and it has not been studied as widely as leukemia or lymphoma, although recent researches brought great improvements in treatment due to immunotherapy and targeted drugs development.

Central Nervous System Cancers

The brain and spinal cord cancers are considered as separate groups because of special localization and behavior. The term "brain cancer" is misleading since brain tumors are classified according to the type of the cells from which they develop:

Gliomas – tumors arising from glial cells (tissue that surrounds neurons in the brain); includes such dangerous tumor as glioblastoma
Meningiomas – tumors developing in the tissues surrounding the brain; usually non-cancerous
Medulloblastomas – tumors arising from the cerebellum and mostly affecting children

No matter whether brain tumors are benign or malignant, the special characteristic of brain cancer is that just its localization is enough to cause severe neurological problems.

Childhood Cancers: A Distinct Category

Pediatric cancer is significantly different from adult cancer in terms of types of diseases and causations. While adult cancer cases have often been caused by lifestyle and environmental risk factors that have accumulated during decades, the cause of childhood cancer is usually genetic, and the location of the disease in body tissues is also different. Some of the most frequent types of childhood cancer are:

Leukemia (especially acute lymphocytic leukemia)
Brain and spinal tumors
Neuroblastoma – originates in immature cells of nervous system and affects only young children
Wilms tumor – renal cancer affecting only young children
Lymphoma

Fortunately, overall survival rates of childhood cancer are significantly higher compared to those of adult cancer.

Which Cancers Are Most Common?

According to the most recent WHO, the cancers diagnosed most frequently in the world— accounting for the large majority of all new cancer cases — are, in ascending order:

Esophageal cancer
Liver cancer
Thyroid cancer
Non-Hodgkin lymphoma
Stomach (gastric) cancer
Colorectal cancer
Prostate cancer
Lung cancer
Breast cancer
Leukemia
Pancreatic cancer

It's worth separating incidence (how many people are diagnosed) from mortality (how many people die from it) — they don't always align. Lung cancer, for instance, causes more deaths annually than colorectal and pancreatic cancer combined, despite not being the most frequently diagnosed cancer, because it's often caught at a later, harder-to-treat stage. Pancreatic cancer, meanwhile, ranks far lower in incidence but has one of the lowest survival rates of any major cancer type, precisely because it's rarely caught early.

Why This Classification Matters for Treatment

Type of cancer, rather than stage, is responsible for the vast majority of all treatment decisions. Treatment of a carcinoma usually involves surgical excision of the mass lesion. In contrast, the treatment of a leukemia, which does not form a mass, is systemic and relies on chemotherapy or targeted drugs given intravenously via the blood circulation. Different types of lymphoma or myeloma require different treatment regimens based on the behavior of the immune cell of this type.

That is also why there has been such an emphasis on precision medicine for cancer therapy during the past decade or so — treatment decisions not only depend on the site where the primary lesion originated but also the specific genetic abnormalities associated with the particular tumor type.

Final Thoughts

"Cancer" does not mean one disease but rather means a family of more than 100 cancers that are all different in their biological natures, development, risk factors, and mode of treatment. Learning the differences between a carcinoma and a sarcoma or leukemia and lymphoma goes far beyond the mere academic knowledge because it helps to realize why two patients with "cancer" can follow totally different paths of treatment. Being diagnosed with a certain kind of cancer means first identifying the type of cancer a person suffers from.