Overview of Cancer | Med

What is Cancer?

Cancer happens when a group of cells in the body starts growing abnormally and no longer follows the body’s normal control system. Instead of stopping when necessary, these cells continue to multiply, invade nearby tissues and sometimes spread to other parts of the body.

As cancer cells grow, they can form a mass called a tumor. However, not all tumors are cancerous. There are:

Benign tumors: non-cancerous and usually do not spread
Malignant tumors (cancer): able to invade nearby tissues and spread to other organs

When cancer spreads from its original location to another part of the body, this process is called metastasis.

Common types of Cancer

Cancer can develop in many different parts of the body. In general, cancer is divided into several main groups:

1. Blood and Immune System Cancers

These include:

Leukemia
Lymphoma

These cancers affect the blood, bone marrow or immune system. Common symptoms may include:

Ongoing fatigue
Swollen lymph nodes
Frequent infections
Unexplained weight loss

2. Carcinoma - Cancer of Organs and Body Surfaces

This is the most common type of cancer. Carcinomas begin in the cells that cover or line:

The skin
Lungs
Stomach
Intestines
Breasts
Thyroid gland
Prostate gland

Examples include:

Lung cancer
Breast cancer
Colorectal cancer
Skin cancer

Carcinomas are more common in older adults.

3. Sarcoma - Cancer of Connective Tissues

Sarcomas develop in:

Bones
Muscles
Blood vessels
Connective tissues

Examples include:

Bone cancer
Muscle cancer

Sarcomas are less common but are more likely to occur in younger people.

Cancer Terminology

The following terms are often used in discussing cancer:

Aggressiveness: The degree to which (or speed at which) a tumor grows and spreads
Benign: Noncancerous. Benign tumors do not invade nearby tissues or spread to distant sites through the bloodstream or lymphatic system (metastasize). However, a benign tumor may still grow in place and cause problems by pressing on nearby tissues.
Carcinogen: An agent that causes cancer
Carcinoma-in-situ: Cancerous cells that are still contained within the tissue where they have started to grow and that have not yet invaded surrounding normal tissue or spread to other parts of the body.
Cure: Complete elimination of the cancer with the result that the specific cancer will not grow back
Differentiation: The extent to which the cancer cells have matured, ceased to multiply, and taken on normal cellular functions so that they no longer look like rapidly multiplying and primitive cells
Grade: The degree of abnormality of the appearance of cancer cells on microscopic examination—more abnormal appearing cells are more aggressive
Invasion: The capacity of a cancer to grow into and destroy surrounding tissue
Malignant: Cancerous cells that can invade adjacent tissue and can also spread to other parts of the body
Malignant transformation: The complex process by which cancerous cells develop from healthy cells
Metastasis: Cancerous cells that have spread to a completely new location
Neoplasm: General term for a tumor, whether cancerous or noncancerous
Recurrence (relapse): Cancerous cells return after treatment, either in the primary location or as metastases (spread)
Remission: Absence of all evidence of a cancer after treatment although there may still be cancer in the body
Stage: The extent to which cancer has spread
Survival rate: The percentage of people who survive for a given period of time after treatment (for example, the 5-year survival rate is the percentage of people who survive 5 years)
Tumor: An abnormal growth or mass

Why is understanding Cancer important?

Hearing the word “cancer” can feel overwhelming and frightening. However, understanding the disease can help patients and families:

Reduce fear and uncertainty
Make informed healthcare decisions
Better support loved ones during treatment

Today, many types of cancer can be treated or managed effectively when detected early and cared for appropriately.

Source: MSD Manuals. “Overview of Cancer”
By Robert Peter Gale, MD, PhD, DSC(hc), Imperial College London
Available at: https://www.msdmanuals.com/home/cancer/overview-of-cancer/overview-of-cancer