Smoking and Cancer: How Smoking Causes Cancer, and What Quitting Does

What cancer is

Cancer is the name for diseases in which abnormal cells divide out of control and can invade other tissues. Cancer cells can spread to other parts of the body through the blood and lymph systems. There are more than 100 types, mostly named for the organ or kind of cell where they begin: lung cancer starts in the lung, laryngeal cancer in the larynx (voice box).

Symptoms can include:

• a thickening or lump anywhere in the body;
• weight loss or gain with no known reason;
• a sore that does not heal;
• hoarseness or a cough that won't go away;
• difficulty swallowing, or discomfort after eating;
• changes in bowel or bladder habits;
• unusual bleeding or discharge;
• feeling weak or very tired.

How smoking leads to cancer

Smoking can both cause cancer and stop the body fighting it:

• It weakens the immune system. Poisons in cigarette smoke make it harder for the body to kill cancer cells, so they keep growing unchecked.
• It damages DNA. Poisons in tobacco smoke can damage or change a cell's DNA, the "instruction manual" that controls its normal growth and work. A cell with damaged DNA can start growing out of control and form a tumour.

Doctors have long known that smoking causes most lung cancers, and it still does: nearly 9 in 10 lung cancer deaths are caused by smoking or by secondhand smoke. People who smoke today are at greater risk of lung cancer than smokers were in 1964, even though they smoke fewer cigarettes — possibly because of changes in how cigarettes are made and the chemicals in them. Treatment is improving, but lung cancer still kills more men and women than any other cancer. In the United States, more than 7,300 people who don't smoke die each year of lung cancer caused by secondhand smoke — the mix of smoke from the burning end of a cigarette and the smoke a smoker breathes out.

Smoking can cause cancer almost anywhere in the body:

• blood (acute myeloid leukaemia);
• bladder;
• cervix;
• colon and rectum;
• oesophagus;
• kidney and renal pelvis;
• larynx;
• liver;
• lungs, trachea and bronchus;
• mouth and throat;
• pancreas;
• stomach.

Men with prostate cancer who smoke may be more likely to die of it than those who don't. Smokeless tobacco, such as chewing tobacco, causes cancer too, including cancers of the oesophagus, mouth and throat, and pancreas.

Prevention: don't smoke, or quit

The most important way to prevent smoking-related cancer is not to smoke, or to quit, and to avoid secondhand smoke. Quitting lowers the risk of 12 cancers — lung, larynx, mouth and pharynx, oesophagus, pancreas, bladder, stomach, colon and rectum, liver, cervix, kidney, and acute myeloid leukaemia.

Screening

Cervical and colorectal cancers. Screening as recommended helps prevent these cancers and finds them early, when treatment is most likely to work. CDC offers free or low-cost cervical cancer screening across the country, and its Screen for Life campaign tells adults why regular colorectal screening matters.

Lung cancer. People who have smoked for many years may consider screening. The only recommended test is a low-dose CT scan, in which an X-ray machine uses low doses of radiation to make detailed pictures of the lungs. The U.S. Preventive Services Task Force recommends a yearly scan for people who:

• have a smoking history of 20 pack-years or more, and
• smoke now or quit within the past 15 years, and
• are 50 to 80 years old.

A pack-year is smoking an average of a pack a day for a year: 20 pack-years could be a pack a day for 20 years, or two packs a day for 10. The task force advises stopping yearly screening once a person has not smoked for 15 years, or develops a health problem that makes them unwilling or unable to have surgery if cancer is found. Talk to your doctor about the benefits and risks. Screening is no substitute for quitting.

Treatment

Treatment depends on the type of cancer and its stage — how severe it is and whether it has spread — and doctors may also weigh the patient's age and general health. Often the aim is a cure; sometimes it is to control the disease or ease symptoms for as long as possible, and the plan can change over time. Most plans involve surgery, radiation or chemotherapy; others use biological therapy, which helps the immune system fight cancer. Some cancers respond best to one treatment, others to a combination.

Patients given very high doses of chemotherapy or radiation may be advised to have a stem cell (bone marrow) transplant, because such doses destroy normal blood cells as well as cancer cells; the transplant helps the body make healthy blood cells again. It is a complicated procedure with many side effects and risks.

Quitting improves the outlook for people with cancer. Those who keep smoking after diagnosis are more likely to die of cancer than non-smokers and more likely to develop a second, new tobacco-related cancer.

Colorectal cancer and ostomies

An ostomy (or stoma) is a surgical opening that lets waste leave the body. It is used in treating cancer and other diseases when the body's normal opening is closed or altered by treatment, and a pouch around the opening collects the waste. Ostomies are usually made early in surgical treatment to remove cancer. For people with colorectal cancer, a colostomy — an opening from the bowel to the abdomen — can save a life. An ostomy may be temporary, while the affected area heals, or permanent, when the whole colon or its end has been removed. The United Ostomy Associations of America offers information on ostomy terms, equipment, daily life with an ostomy, food and nutrition, and support groups.

A story from Tips

Terrie H. smoked for 30 years and was diagnosed with cancer 10 times. She started smoking young, and she came to believe that much of what she went through could have been prevented. CDC's Tips From Former Smokers campaign tells her story and those of others living with cancer caused by smoking.

Free help to quit

• Call 1-800-QUIT-NOW. Help is also available in Spanish (1-855-DÉJELO-YA), Chinese (1-800-838-8917), Korean (1-800-556-5564) and Vietnamese (1-800-778-8440).
• Text QUITNOW to 333888 (message and data rates may apply), or use CDC's quitSTART app.

Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.

Sources

• Centers for Disease Control and Prevention, "Smoking and Cancer," Tips From Former Smokers. https://www.cdc.gov/tobacco/campaign/tips/diseases/cancer.html
• National Cancer Institute, "What Is Cancer?" https://www.cancer.gov/about-cancer/understanding/what-is-cancer