Cancer 101: A Reference Guide

Cancer 101: A Reference Guide

Reviewed by Jasper Clinical Board

Last updated 5/24/21

Though an estimated one-third of all people will get cancer during their lifetime, the diagnosis is not the same across the board. That’s because “cancer” is not one disease, but instead a group made of hundreds of different diseases.
Cancer can develop anywhere in the body. It starts when abnormal cells take root in the body and divide uncontrollably, crowding out and destroying healthy cells in the body. These abnormal cells may form a mass of tissue called a tumor; in some cancers, such as leukemia, tumors do not form but instead the abnormal cells float through the bloodstream, crowding out healthy blood cells and platelets.
Some of the most common types of cancer include:
Breast cancer, which forms in the cells of the breasts and surrounding tissues.
Prostate cancer, which forms in a man’s prostate (the walnut-sized gland that produces seminal fluid).
Basal cell cancer, a common type of skin cancer that most often develops on areas of skin exposed to the sun.
Melanoma, the most serious type of skin cancer that forms in the skin’s pigment-producing cells known as melanocytes.
Colon cancer, located in the digestive tract’s lower end.
Lung cancer, which forms in the lungs.
Leukemia, a cancer of blood-forming cells that ultimately hinders the body’s ability to fight infection.
Lymphoma, a cancer that begins in the infection-fighting cells of the immune system, called lymphocytes.
Once a doctor has identified the presence of cancer, further tests known as pathology reports can provide critical details about the diagnosis. These reports break down the specific details about your cancer and how it is acting in your body.

Understanding Your Cancer Diagnosis



Staging describes not only where a cancer is located, but whether it is affecting other parts of the body. Sometimes cancer cells stay contained to the primary tumor, while other times the cancer spreads to other areas of the body (metastasizes). Your medical team may use blood tests, imaging scans, and/or surgeries to determine whether your cancer is contained to the tumor (noted as “T”); has spread to the lymph nodes (noted as “N”); or metastasized, or spread, to other parts of the body (noted as “M”). In the pathology report, additional letters and numbers may be assigned to the T, N, and M score to provide even more detail on the specific cancer. Doctors will use the TNM results to determine what stage a person is in:
Stage 0: Cancer in situ (“in place”). Stage 0 cancers are still located in the place they started and have not spread to nearby tissues.
Stage I:  A small cancer or tumor that has not grown deeply into nearby tissues, spread to the lymph nodes, or metastasized to other parts of the body.
Stage II: The cancer or tumor is larger, but has not spread to lymph nodes and/or surrounding tissues.
Stage III: The cancer or tumor is larger and may have spread to the lymph nodes and/or surrounding tissues.
Stage IV: The cancer has spread from where it started to at least one other body organ; this is also known as “secondary” or “metastatic” cancer. When a cancer metastasizes to a different part of the body, it is still defined by its original location. For example, if colon cancer metastasizes to the lungs, it is still referred to as colon cancer, not lung cancer.
Typically, blood cancers (other than lymphomas) are not staged, because by nature your blood circulates throughout your body, so staging is not useful to your doctor. 


Tumor grades are assigned based on how fast biopsied tissue from the tumor appears to grow under a microscope. Unlike stages, which provide a snapshot of where the cancer is in the body, tumor grades indicate how quickly a tumor is likely to grow and spread:
Grade 1: Tumor cells and the organization of the tumor tissue appear close to normal, indicating slow growth.
Grade 2: Cells are somewhat abnormal and will grow faster than normal cells.
Grade 3: Cells and tissue look abnormal and are disorganized, indicating they will grow  rapidly.
Grade 4: The most abnormal-looking cells with a high level of disorganization, indicating they will grow and spread aggressively.

Risk Group

For some cancers, doctors will include a risk group designation as part of a cancer diagnosis. Typically, these groups are labeled low, medium, and high, and correspond with how likely it is that the cancer will come back. These designations can help guide treatment selection.

Tumor Markers

Tumor markers, also known as biomarkers, are substances found in the blood, urine, or tissues of some people with cancer. These substances are usually proteins made by the tumor itself, or made by healthy cells in response to the tumor. Your doctor may order tests to see if you have these substances in your body, and if so, what amounts are present.
Tumor markers or genetic tests, like FISH (fluorescence in-situ hybridization) testing, flow cytometry, or genomic sequencing (Sanger or Next Generation Sequencing) can provide your doctor with important information about your cancer and how to treat it. These tests also provide a baseline for your medical team to refer to during treatment to determine how your cancer is responding.

You are More Than a Number

Though the criteria used to make a cancer diagnosis can feel clinical and impersonal, these numbers are actually a way to distinguish you as an individual. Based on the information gathered, your medical team will work with you to develop a treatment plan that’s best for you.
Some people like to take an active role in this process by asking about the available treatment options, the success rate of each treatment, and what side effects to expect. Others prefer to place their trust in their medical team and simply show up at their appointments. The care and treatments you receive should align with your individual values, preferences, and priorities. In other words, the best way to participate in your care is the way that feels right to you.

The content on this website is intended to provide the best possible information for you, but should not be considered—or used as a substitute for—medical advice. If you have questions about your diagnosis or treatment, please contact your health care provider(s). For questions or comments about this content, please email us at