Cancer Basics

Hearing the word "cancer" changes life in an instant. It brings up many emotions. You likely have many questions. Understanding the basics of cancer can help you feel more in control. This article explains what cancer is and how it starts. It also covers common risk factors and symptoms. You will learn how doctors stage cancer and what the outlook often looks like.

Who is affected by cancer?

Cancer is not just 1 disease. It is a group of more than 100 related diseases. It can start almost anywhere in the human body.¹

Anyone can get cancer. However, certain things increase the chance of getting it. These are called risk factors. Having a risk factor does not mean you will definitely get cancer. Many people with risk factors never get it.¹

Causes and risk factors

Age is one of the most significant risk factors for most cancers. The risk goes up as you get older. In fact, 88 percent of people diagnosed with cancer in the United States are age 50 or older.²

Lifestyle choices also play a role. Tobacco use is a leading cause of cancer and death from cancer. Drinking alcohol can also raise your risk. Being overweight or having obesity is linked to a higher risk for several types of cancer.²

Some risk factors are out of your control. You might inherit changes in your genes from your parents. These genetic changes can make you more likely to develop cancer. Your environment matters too. Exposure to things like ultraviolet (UV) radiation from the sun or certain chemicals can damage your DNA.²

How does cancer develop?

Your body is made up of trillions of cells. Normal cells grow and divide to form new cells. When they grow old or get damaged, they die. New cells then take their place.^1,2

Cancer breaks this orderly process. It starts when genetic changes interfere with this process. Cells start to grow uncontrollably. These abnormal cells do not die when they should. They build up and form a mass of tissue called a tumor.^1,2

Not all tumors are cancerous. Benign tumors do not spread into nearby tissues. Malignant tumors are cancerous. They can invade nearby tissues. Cancer cells can also break away and travel to other parts of the body. This spread is called metastasis.^1,2

Signs and symptoms of cancer

Signs of cancer depend on where it is in the body. Some cancers do not show symptoms right away. Others can cause changes that you might notice.^1,2

Common signs and symptoms include:²

• Fatigue – Feeling extremely tired even after resting
• Lumps – A thickening or lump under the skin
• Weight changes – Unexplained weight loss or gain
• Skin changes – New moles, sores that do not heal, or changes in skin color
• Pain – Pain that does not go away
• Changes in habits – Trouble with bowel movements or urination

Cancer statistics

Cancer is very common in the United States. It is the second leading cause of death after heart disease.³

Researchers estimate the number of new cancer cases each year. For 2024, the American Cancer Society expected about 2 million new cancer cases in the United States. This number does not include some skin cancers.³

The risk of developing cancer varies by gender. Approximately 1 in 2 men will develop cancer in their lifetime. For women, the risk is about 1 in 3.³

Stages of cancer/cancer progression

Doctors use a system called staging to describe cancer. Staging helps the healthcare team understand how much cancer is in the body. It tells them if the cancer has spread. This information is vital for planning the best treatment.⁴

Most doctors and healthcare centers use the TNM system as their standard cancer staging method (some cancers have specific, alternative methods). This stands for tumor, node, and metastasis:⁴

• T (Tumor) – Describes the size of the main tumor
• N (Node) – Describes if cancer has spread to nearby lymph nodes
• M (Metastasis) – Describes if cancer has spread to other parts of the body

These details help assign a specific stage. Stages are usually numbered from 0 to 4:⁴

• Stage 0 – Abnormal cells are present but have not spread. This is often called "carcinoma in situ."
• Stages 1, 2, and 3 – Cancer is present. The higher the number, the larger the tumor. It also means it has spread more into nearby tissues or lymph nodes.
• Stage 4 – The cancer has spread to distant parts of the body. This is the most advanced stage.

Cancer prognosis, life expectancy, and outlook

The outlook for people with cancer has improved greatly. This is due to better screening and new treatments. Fewer people are dying from cancer today compared to the past. The cancer death rate has dropped by 33 percent since 1991.⁵

Doctors often use a number called the "5-year relative survival rate." This compares people with the same type and stage of cancer to people in the overall population. It estimates how likely it is that people with cancer will be alive 5 years after diagnosis.⁵

Survival rates vary for each person. They depend on the type of cancer and its stage. Your age and overall health also affect the outlook.⁵

Many people are living with a history of cancer today. In fact, there are more than 18 million people estimated to be living with cancer in the United States.⁵

A life-changing diagnosis

A cancer diagnosis is life-changing. However, knowledge is a powerful tool. Understanding the causes, symptoms, and stages helps you navigate this journey. Survival rates are improving every year. New treatments offer hope to many people. Talk to your healthcare team about your specific situation. They can provide the best guidance for your care.⁵