Common and Rare Cancer Types and Oncology Terms Explained

Cancer is not a single disease; it has more than 150 main types , exceeding 1000 with subtypes. Many, though not all, are well classified. Several methods exist, and understanding them helps explain cancer and its terminology. This comprehensive article summarizes common and rare cancer types.

How are cancer types classified?

Cancers are commonly distinguished in 3 ways:

• The cell or tissue type in which cancer begins
• The organ or organ system where it develops
• The genetic change triggering cancer (a very new classification method)

Broadly, cancers fall into two groups:

1. Blood and bone marrow cancers (hematological malignancies): leukemia (blood cancer), lymphoma (lymph cancer) and myeloma are examples
2. Solid (organ-based) cancers: all cancers other than blood cancers. Most are named after their organ of origin, such as breast, lung or prostate cancer.

Primary cancer or metastasis?

Metastasis is spread from the original site to other tissues and organs. The site where cancer began before spreading is called the primary cancer . Breast cancer spreading to the lung is therefore primary breast cancer metastatic to the lung. Rarely, in advanced cancer, distinguishing the primary site from metastases becomes difficult.

Distinguishing noncancerous (benign) from cancerous (malignant) tumors can also very rarely be difficult. Usually, however, clear differences exist. The most important difference is malignant tumors’ potential to spread. Cancer and healthy cells differ substantially; cancer cells do not grow normally but divide and proliferate continuously.

- What are lung cancer metastasis symptoms?

Cancers by cell or tissue type

Many cancers are named for their cell of origin. Understanding these main types helps after diagnosis. For example, in kidney cancer, cell type provides substantial information about the tumor and prognosis.

There are 6 main cancer types by cell type:

1. Carcinomas (adenocarcinoma, squamous cell carcinoma, basal cell carcinoma, transitional cell carcinoma)
2. Sarcomas (osteosarcoma, soft tissue sarcoma)
3. Myelomas
4. Leukemias
5. Lymphomas
6. Mixed types (including blastomas)

What is carcinoma?

Carcinomas are the most common cancers, accounting for 80-90% of all cases. They arise in epithelial cells. These have three types—covering, glandular/secretory and sensory—and broadly line the body’s inner and outer surfaces, occurring in skin, cavities and organs. This tissue therefore directly contacts carcinogens . Epithelial cells also divide more frequently than connective/soft tissue cells.

Direct carcinogen contact and frequent division explain why most cancers arise in this tissue!

Carcinomas can be divided into:

• Adenocarcinomas: These begin in glandular epithelial cells producing liquids such as breast milk.
• Squamous cell carcinomas: Examples of squamous/flat cells occur in the skin’s upper layer, esophagus, upper airways, cervix and lower vagina.
• Basal cell carcinomas: Basal cells occur only in skin and form its deepest cell layer.
• Transitional cell carcinomas: Transitional cells are epithelial cells most commonly in the urinary tract: bladder and kidney collecting ducts.

What is sarcoma?

Sarcomas arise from mesenchymal cells and are cancers of bone and soft tissues. They include cancers of bone, muscle, tendons, ligaments, cartilage, blood vessels, nerves, synovial (joint) tissue and fat. These tissues divide much less than epithelial cells, so sarcomas are far rarer.

Examples include:

• Osteosarcoma (bone cancer): Osteocytes are bone cells.
• Chondrosarcoma (cartilage cancer): Cartilage cells are called chondroblasts.
• Liposarcoma (fat tissue cancers)
• Rhabdomyosarcoma (skeletal muscle cancer)
• Leiomyosarcoma (smooth muscle cancer)
• Angiosarcoma (blood vessel cancers)
• Mesothelioma (pleural malignant mesothelioma = cancer of the lung lining, peritoneal malignant mesothelioma = cancer of the abdominal lining)
• Fibrosarcoma (fibrous tissue cancers)
• Glioma and astrocytoma (connective tissue cells in the brain)

What is myeloma?

Multiple myeloma is cancer of immune cells called plasma cells, which produce antibodies.

What is leukemia?

Leukemias are cancers of blood cells. These develop in bone marrow, so blood cancers involve marrow. Unlike myelomas and lymphomas, leukemias are considered liquid cancers among hematological cancers.

Their main treatment is chemotherapy delivered intravenously directly into the blood.

The most common leukemia types:

• Acute lymphocytic leukemia (ALL): Cancer of white blood cells called lymphocytes.
• Chronic lymphocytic leukemia (CLL)
• Acute myelocytic leukemia (AML): Cancer of mature or immature white blood cells called myelocytes, such as neutrophils.
• Chronic myelocytic leukemia (CML)

- What are blood cancer symptoms?

Differentiation and mixed types

All our cells originate from a single zygote formed by a father’s sperm and mother’s egg. It divides in two, then each resulting cell divides again: 2-4-8-16 … Cells then begin differentiation to form specific tissues and organs. A primitive/stem cell is poorly differentiated; a normal cell is well differentiated and belongs to a particular tissue, such as skin, blood or nerve. Another way to classify cancer cells is by their resemblance to the tissue of origin. Tumor cells may therefore be well differentiated or poorly differentiated (undifferentiated) . Generally, well-differentiated cells, resembling normal cells in their organ, have milder biology, while poorly differentiated cells behave more aggressively.

Tumors may also be heterogeneous/mixed. Lung tumor cells, for example, may resemble both adenocarcinoma and squamous cell carcinoma. The pathology report may describe adenosquamous features. Another type is blastoma: cancers arising in embryonic precursor cells, more common in children. Examples include nephroblastoma, medulloblastoma and retinoblastoma. The suffix -blastoma indicates a tumor of primitive, incompletely differentiated or precursor cells.

What cancer types occur by organ system?

Cancers are usually classified by the organ or organ system of origin. Examples include:

Central nervous system cancer

These cancers arise in brain or spinal cord tissue. Most cancers in the brain, however, are metastases from other organs; metastatic brain tumors are 7 times as common as primary brain cancers. Lung, breast and malignant melanoma skin cancers most often spread to the brain.

Unlike tumors elsewhere, primary brain cancer generally does not spread outside the brain. The most common types are glioblastoma multiforme (GBM-4) and astrocytomas.

- What are benign and malignant brain tumors? What does tumor grade mean? What types are there?

Head and neck cancers

Head and neck cancers can affect the tongue, larynx or any head and neck region. Main causes include alcohol, smoking, heavy consumption of hot drinks and human papillomavirus (HPV) infection

- What is HPV – human papillomavirus, and how does it cause cancer?

Breast cancer

Breast cancer is very common in women, but can also affect men: approximately every 150 female cases correspond to 1 male case. The most common type is invasive ductal carcinoma.

- Breast cancer can also occur in men.

Sometimes breast cancer is detected before becoming invasive (spreading within the breast). This is called carcinoma in situ or stage 0 breast cancer.

Lung cancer

Lung and bronchial cancer remain the leading cancer causes of death in both men and women worldwide. Smoking is undoubtedly the main cause (90%), but never-smokers also develop them.

- Causes of lung cancer other than smoking

Main lung cancer subtypes:

• Non-small cell lung cancer: Of all lung cancers, 85%. Subtypes include adenocarcinoma, squamous cell, large cell and mixed types.
• Small cell lung cancer: It accounts for approximately 15% of lung cancers and almost never occurs in never-smokers.
• Mesothelioma: Cancer of the lung lining, strongly associated with asbestos exposure.

- Small cell and non-small cell lung cancer – What are the differences?

Digestive system cancers

Digestive tract cancers can occur anywhere from mouth to anus. Most are adenocarcinomas. Squamous cell carcinomas occur in the upper esophagus and outer anus.

Types include: 

• Esophageal cancer: Incidence has increased in recent years, possibly due to rising obesity rates.
• Gastric cancer: Common worldwide.
• Pancreatic cancer: Less common than other cancers, but among the leading 10 causes of cancer death worldwide in women and men.
• Liver cancer: Primary cancer arising in the liver is rare; metastases to the liver are more common. Main risk factors include alcohol and chronic hepatitis B or C infections.
• Colon cancer: Often called colorectal cancer, including colon and rectal cancers. It is the third most common cancer in both women and men.
• Anal cancer: Differs from colon cancer in treatment and causes. HPV infection is now a major cause of most anal cancers.

Genitourinary system cancers

This system includes kidneys, bladder, ureters connecting kidneys to bladder, urethra carrying urine outside, and the prostate.

Subtypes include:

• Kidney cancer: Common types are renal cell carcinoma, transitional cell carcinoma and Wilms’ tumor in children. 
• Bladder cancer: Approximately half are caused by smoking. People working with dyes are also at increased risk. 
• Prostate cancer: The second leading cause of cancer death in men, although five-year survival is now around 90%.

Reproductive system cancers

Reproductive organ cancers affect both women and men.

Subtypes include: 

• Testicular cancer
• Ovarian cancer (including germ cell tumors) 
• Uterine cancer (endometrial cancer)
• Fallopian tube cancer 
• Cervical cancer

Endocrine cancers

Most endocrine cancers other than thyroid cancer are very rare. The endocrine system consists of hormone-producing glands, and these cancers cause symptoms of excessive or insufficient hormone production. 

Thyroid cancer: A common cancer, more frequent in women. Fortunately, most are now diagnosed early and treated effectively.

Bone and soft tissue cancers

These affect bones and soft tissues such as muscles, ligaments, fibrous tissue and even blood vessels. Primary bone and soft tissue cancers are rare, but bone metastases are common. Primary or metastatic bone cancer usually presents with pain or pathological fractures.

Subtypes include:

• Osteosarcoma (bone cancer)
• Kaposi sarcoma: A soft tissue cancer usually occurring in people with HIV / AIDS. 
• Ewing sarcoma: A bone cancer mainly affecting children.

- What are bone metastases? Why do cancers spread to bone, and how are they treated?

Blood-related cancers

These include cancers of blood cells and solid immune tissues such as lymph nodes. Environmental factors and viruses, such as Epstein-Barr virus, play important roles in risk. Blood and bone marrow cancers are the most common childhood cancers.

• Hodgkin lymphoma 
• Non-Hodgkin lymphoma
• Acute lymphocytic leukemia (ALL)
• Chronic lymphocytic leukemia (CLL) 
• Acute myelogenous leukemia (AML)
• Chronic myelogenous leukemia (CML)
• Myeloma

Skin cancers

Skin cancers are generally divided into melanoma and nonmelanoma types. Nonmelanoma cancer is more common. Melanoma causes most skin cancer deaths, but since 2012, immunotherapies and targeted drugs have greatly improved its treatment outcomes.

Subtypes: 

• Melanoma 
• Squamous cell carcinoma of the skin 
• Basal cell carcinoma of the skin

What other tools classify cancers?

Besides cell type, differentiation and organ of origin, cancers are classified in other ways.

• Tumor grade: Grade measures aggressiveness. Grade 1 tumors are not aggressive and resemble normal cells of origin. Grade 3 tumors are generally more aggressive and look more different from normal cells.
• Tumor stage: Tumors are staged in various ways, usually numbered 1 to 4; stage rises as size and/or spread increases.
• Hereditary and nonhereditary cancer: Some cancers are hereditary, triggered by germline mutations inherited from one or both parents. They are less common than believed: approximately 5-10% of all cancers.

Familial, Hereditary and Sporadic: Frequently Confused Concepts in Cancer

• DNA analysis / molecular profile: With genetic advances, tumors are increasingly classified by genetic characteristics. Some lung cancers have EGFR mutations, for example, while others have ALK rearrangements.

What is whole exome sequencing and genome sequence analysis?

What are rare cancers?

Many cancer types are rare, affecting only a few people each year. Hundreds of varieties exist. Rare cancers can be described as subtypes of common cancers. As doctors and researchers learn more, we define subtypes by specific features and differences. This classification can be our greatest aid in selecting treatment. Some subtypes are rare. Experience may make an important difference in managing them, so seeking a second opinion after a rare cancer diagnosis is useful.

Examples of rare cancers: 

• Angiosarcoma
• Merkel cell skin cancer 
• Desmoid tumor
• Fibromyxoid sarcoma
• Uterine leiomyosarcoma
• Erdheim-Chester disease

- Genetic tests for rare cancers enable new treatments

Causes, symptoms and treatments of different cancers

Cancer has many causes and risk factors, some more important for particular types. Heavy, prolonged asbestos exposure causes mesothelioma, for example. Breast cancer may be hereditary or have other causes.

• What, briefly, are the causes of cancer?
• When does a cancer-causing substance cause cancer?

In conclusion, recognizing cancer symptoms and undergoing cancer screening for cancers detectable early are essential for successful treatment. The first requirement for the best treatment plan is correctly identifying cancer type and stage.

- WHAT IS CANCER? Why and how does it develop? The entire process in brief!