By printing and/or reading this article, you agree that you accept all terms and conditions of use, as specified online.

Cancer: What It Is

Note: Links to specific cancers can be found at the end of this article.

Health NewsEvery day, without our even being aware of it, the cells that make up our body are growing, dividing and/or producing more cells as needed in order to keep us healthy. But sometimes, this process goes haywire; certain cells lose their normal control mechanism and start growing out of control. This is what happens with cancer.

Tumors and cancer are not always the same thing. The National Cancer Institute (NCI) says a tumor is a mass of extra tissue. Some tumors can be felt or seen externally on the body. Some tumors are internal and can be picked up via an imaging scan. NCI says tumors can be benign or malignant.

According to the American Cancer Society (ACS), most cancers form as a tumor. But some do not. For example, the cancer cells of leukemia involve the blood and blood-forming organs, but do not actually form a mass or tumor.

Types of cancer

Cancer can begin in any part of the body, and is categorized by the type of tissue where it starts.

Cancers are usually identified by their site of origin. That means that the type or name of the cancer is the original site where the cancer developed, even if the cancer has spread to other parts of the body. For example, even if breast cancer has spread to the liver, it would still be considered breast cancer, not liver cancer. (Read about "Liver Cancer")

In some cases, ACS says the cancer first appears in one or more of the sites to which it has spread, and the original site where the cancer developed is not known. These cancers are called Cancers of Unknown Primary. Sometimes, additional tests can determine where the cancer started, and the cancer would be renamed for its site of origin. Other times, the primary site may never be known. ACS says that even if the source is never discovered, treatment can still be successful.

Causes and risk factors

In many cases, the exact cause of the cancer is unknown. However, we do know that there are some things that can increase the risk of different types of cancer. (Read about "Reduce Cancer Risks") Among the things that can affect a person's risk of developing cancer, according to the American Cancer Society are:

In addition, cancer can be more likely to develop when the immune system isn't functioning properly. (Read about "Primary Immunodeficiency" "Immune System Glossary" "The Immune System")

Finding and staging cancer

The American Cancer Society says many forms of cancer are treated most successfully when caught early. This is why regular screenings, such as Pap tests, mammograms, PSA tests, etc., are so important. (Read about "Cancer Check-ups" "Mammograms")

If a screening produces a suspicious result, or if a doctor suspects cancer for some other reason, additional tests can be done, for example, blood or urine tests or imaging scans.

However, for cancers, the way to make a definitive diagnosis is a tissue diagnosis with a biopsy. Biopsy is the removal of cells or tissues for examination by a specialist physician called a pathologist. The pathologist may study the tissue under a microscope or perform other tests on the cells or tissue. Examination of suspicious cells through a biopsy helps the doctor determine if the cells are malignant (cancerous) or benign. (Read about "Biopsy")

If cancer is present, a doctor must determine what type of cancer it is, how fast it is growing, and whether or not it has invaded nearby healthy tissue or spread to other parts of the body. This helps the doctor determine at what stage the cancer is, and how best to treat it.

Staging is the term used to describe the extent or severity of an individual's cancer. A cancer's stage depends on different factors, including its location, its size, whether lymph nodes have been affected and whether or not the cancer has spread. (Read about "The Lymph System")

NCI says different tests can be used to help determine a cancer's stage. These include blood and urine tests; imaging tests such as x-rays, CT scans, MRI, PET and ultrasound (Read about "X-rays" "CT Scan - Computerized Tomography" "MRI - Magnetic Resonance Imaging" "PET - Positron Emission Tomography" "Ultrasound Imaging"); pathology reports from the biopsy; and surgical reports. Knowing a cancer's stage helps to determine the best way to treat it. (Read about "Cancer Treatments")

Metastasis and angiogenesis

When a cancer spreads to another part of the body, it is called metastasis. Researchers say one of the most important things required for metastasis to occur is the growth of a new network of blood vessels. This process of forming new blood vessels is called angiogenesis. Angiogenesis is a normal biological process. For example, angiogenesis is necessary for the repair or regeneration of tissue during wound healing. Tumor angiogenesis, however, is different. NCI says tumor angiogenesis is the growth of a network of blood vessels that penetrates into cancerous growths, supplies them with nutrients and oxygen and removes waste products. NCI says tumor angiogenesis starts with cancerous tumor cells releasing molecules that send signals to activate genes in the host tissue that, in turn, make proteins to encourage growth of new blood vessels. Certain molecules can either activate or inhibit angiogenesis. Studies are now examining the effectiveness of drugs aimed at inhibiting angiogenesis in specific cancers. (Read about "Clinical Studies")

Below, in alphabetical order, is a list of individual cancers and tumors. You can learn more about each of them by following the appropriate link.

Acute lymphocytic leukemia (ALL): see Leukemia

Acute myeloid leukemia (AML): see Leukemia

Acute nonlymphocytic leukemia (ANLL): see Leukemia

Adenocarcinoma, esophagus: see Esophagus Cancer

Adenocarcinoma, vaginal: see Vaginal Cancer

Adenocarcinoma, bladder: see Bladder Cancer

Anaplastic thyroid cancer: see Thyroid Cancer

Angiosarcoma, liver: see Liver Cancer

Astrocytomas: see Brain Tumors

Basal cell cancer: see Skin Cancer

Bladder cancer: see Bladder Cancer

Bone cancer: see Bone Cancer

Bone cyst, unicameral: see Bone Tumors - Benign

Brain stem gliomas: see Brain Tumors

Brain tumors: see Brain Tumors

Breast cancer: see Breast Cancer

Cervical cancer: see Cervical Cancer

Chest tumors: see Chest Tumors

Children's cancer: see Cancer & Children

Cholangiocarcinoma, liver: see Liver Cancer

Chondrosarcoma: see Bone Cancer

Chronic lymphocytic leukemia (CLL): see Leukemia

Chronic myeloid leukemia (CML): see Leukemia

Colon cancer: see Colorectal Cancer

Colorectal cancer: see Colorectal Cancer

Craniopharyngiomas: see Brain Tumors

Ductal carcinoma: see Breast Cancer

Endometrial cancer: see Uterine Cancer

Ependymomas: see Brain Tumors

Epithelial carcinoma: see The Ovaries

Esophagus cancer: see Esophagus Cancer

Ewing's sarcoma: see Bone Cancer

Eye cancer: see Eye Cancer

Fibrous dysplasia: see Bone Tumors - Benign

Follicular thyroid cancer: see Thyroid Cancer

Gastric cancer: see Stomach Cancer

Germ cell tumors, brain: see Brain Tumors

Giant cell tumor: see Bone Tumors - Benign

Head cancer: see Head & Neck Cancers

Hepatoblastoma,: see Liver Cancer

Hepatocellular carcinoma: see Liver Cancer

Hodgkin's disease: see Lymphoma

Hypopharyngeal cancer: see Head & Neck Cancers

Intraocular cancers: see Eye Cancer

Kidney cancer: see Kidney Cancer

Laryngeal cancer: see Head & Neck Cancers

Leukemia: see Leukemia

Lip cancer: see Oral Cancer

Liver cancer: see Liver Cancer

Lobular carcinoma: see Breast Cancer

Lung cancer: see Lung Cancer

Lymphoma: see Lymphoma

Malignant melanoma: see Skin Cancer

Medullary thyroid cancer: see Thyroid

Medulloblastomas: see Brain Tumors

Melanoma: see Skin Cancer

Mesothelioma: see Mesothelioma

Metastatic squamous neck cancer with occult primary: see Head & Neck Cancers

Multiple myeloma: see Multiple Myeloma & Plasmacytoma

Myelodysplastic Syndromes: see Myelodysplastic/Myeloproliferative Diseases

Myeloma: see Multiple Myeloma & Plasmacytoma

Myeloproliferative Disorders: see Myelodysplastic/Myeloproliferative Diseases

Nasal cavity cancer: see Head & Neck Cancers

Nasopharyngeal cancer: see Head & Neck Cancers

Neck cancer: see Head & Neck Cancers

Neuroblastoma: see Cancer & Children

Neuroectodermal tumors: see Brain Tumors

Non-Hodgkin's lymphoma: see Lymphoma

Oligodendrogliomas: see Brain Tumors

Oral cancer: see Oral Cancer

Orbital cancers: see Eye Cancer

Oropharyngeal cancer: see Head & Neck Cancers

Osteoid osteomas: see Bone Tumors - Benign

Osteosarcoma: see Bone Cancer

Ovarian cancer: see The Ovaries

Paget's disease of breast: see Breast Cancer

Pancreatic cancer: see Pancreatic Cancer

Papillary thyroid cancer: see Thyroid Cancer

Paranasal sinus cancer: see Head & Neck Cancers

Parathyroid cancer: see Parathyroid Glands

Penile cancer: see Penile Cancer

Pineal region tumors: see Brain Tumors

Pineoblastoma: see Brain Tumors

Pineocytoma, brain: see Brain Tumors

Plasmacytoma: see Multiple Myeloma & Plasmacytoma

Prostate cancer: see The Prostate

Rectal cancer: see Colorectal Cancer

Renal cell carcinoma: see Kidney Cancer

Retinoblastomas: see Cancer & Children

Rhabdomyosarcomas: see Cancer & Children

Salivary cancer: see Head & Neck Cancers

Skin cancer: see Skin Cancer

Squamous carcinoma, vaginal: see Vaginal Cancer

Squamous cell carcinoma, skin: see Skin Cancer

Squamous cell carcinoma, bladder: see Bladder Cancer

Squamous cell carcinoma, esophagus: see Esophagus Cancer

Stomach cancer: see Stomach Cancer

Testicular cancer: see Testicular Cancer

Thyroid cancer: see Thyroid Cancer

Tracheal tumors: see Tracheal Tumors

Transitional cell carcinoma, bladder: see Bladder Cancer

Unicameral bone cyst: see Bone Tumors - Benign

Urethral Cancer: see Urethral Cancer

Uterine cancer: see Uterine Cancer

Vaginal Cancer: see Vaginal Cancer

Wilms' tumor: see Kidney Cancer

All Concept Communications material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.

© Concept Communications Media Group LLC

Online health topics reviewed/modified in 2020 | Terms of Use/Privacy Policy

By printing and/or reading this article, you agree that you accept all terms and conditions of use, as specified online.