Cancer: Signs, Causes and Treatment

What cancer is

Cells normally grow, divide and die in a controlled way. Cancer begins when changes (mutations) in a cell's DNA disrupt these controls. The cell divides when it should not and does not die when it should. Over time, more mutations accumulate, and the abnormal cells:

• form a mass (tumor), except in blood cancers
• invade surrounding tissue
• enter blood or lymph vessels and spread to distant organs (metastasis)

Not every tumor is cancer. Benign tumors, such as lipomas or fibroids, do not invade or spread. Malignant tumors do.

Main types of cancer

Warning signs of cancer

Most of these symptoms are usually caused by something less serious, but if they persist for 3 weeks or more, see a doctor:

• a new lump or swelling anywhere
• unexplained weight loss or loss of appetite
• a change in bowel habits or blood in the stool
• unusual bleeding: coughing blood, blood in urine, bleeding between periods or after menopause
• a persistent cough or hoarseness
• difficulty swallowing or persistent indigestion
• a mole that changes in size, shape or color, or a sore that does not heal
• persistent pain with no obvious cause, including night pain
• night sweats or unexplained fevers
• extreme tiredness that does not improve with rest
• changes in the breast: a lump, skin dimpling, nipple changes or discharge

Causes and risk factors

Cancer usually results from a mix of factors acting over many years:

About 4 in 10 cancer cases in the US are linked to modifiable risk factors.

How cancer is diagnosed

• History and examination
• Imaging: X-ray, ultrasound, CT, MRI and PET scans locate tumors and check for spread
• Blood tests: blood counts and tumor markers (such as PSA or CA-125), which support but rarely confirm a diagnosis
• Endoscopy: colonoscopy, upper endoscopy or bronchoscopy to look inside organs
• Biopsy: a tissue sample examined under a microscope. This is the only way to confirm most cancers
• Molecular testing of the tumor, which identifies mutations that targeted treatments can act on

Staging

Staging describes how far the cancer has spread, guiding treatment and outlook. Many solid cancers use the TNM system (tumor size, lymph node involvement, metastasis), summarized as stages 0 to IV. Stage IV means spread to distant organs.

Cancer treatment

Treatment is tailored to the cancer type, stage, genetic features and the person's health and wishes. Common options, often combined:

• Surgery to remove the tumor and nearby lymph nodes
• Radiation therapy: high-energy beams that kill cancer cells in a targeted area
• Chemotherapy: drugs that kill rapidly dividing cells throughout the body
• Immunotherapy: drugs that help the immune system recognize and attack cancer, such as checkpoint inhibitors
• Targeted therapy: drugs aimed at specific mutations or proteins in cancer cells
• Hormone therapy: for hormone-sensitive breast and prostate cancers
• Stem cell transplant for some blood cancers
• Palliative care: symptom control and support at any stage, alongside other treatments

Treatment is usually planned by a multidisciplinary team. Clinical trials offer access to new treatments.

Screening

Screening finds cancer before symptoms appear, when treatment is most effective. US recommendations (USPSTF) include:

• Breast: mammograms every 2 years from age 40 to 74
• Cervical: Pap or HPV testing from 21 to 65
• Colorectal: from age 45 to 75, by colonoscopy, stool tests or other methods
• Lung: yearly low-dose CT for adults 50 to 80 with a significant smoking history
• Prostate: a shared decision about PSA testing for men 55 to 69

Ask your doctor what is right for your age and risk.

Prevention

• do not smoke or use tobacco, and avoid secondhand smoke
• limit alcohol
• keep a healthy weight and be physically active
• eat plenty of vegetables, fruit, whole grains and fiber, and less processed meat
• protect your skin from the sun and avoid tanning beds
• get vaccinated against HPV and hepatitis B
• test your home for radon
• attend recommended screenings

Outlook

Survival has improved greatly over recent decades. Outlook varies widely by type and stage: many early-stage cancers have high cure rates, and many advanced cancers can now be controlled for years. Cancer survivors may need follow-up for recurrence and late effects of treatment.

Frequently asked questions

What are the early warning signs of cancer?

Common warning signs include a new lump, unexplained weight loss, a change in bowel or bladder habits, unusual bleeding, a persistent cough or hoarseness, difficulty swallowing, a changing mole, a sore that does not heal, and persistent unexplained pain or fatigue. See a doctor if any lasts 3 weeks or more.

What causes cancer?

Cancer is caused by DNA changes that make cells grow uncontrollably. These changes can be triggered by tobacco, alcohol, UV light, some infections, radiation, chemicals and excess body weight, or inherited. Age is the biggest risk factor, because changes accumulate over time.

Can cancer be cured?

Many cancers can be cured, especially when found early. Others can be controlled for many years with treatment. Cure rates depend on the cancer type, stage, genetic features and response to treatment.

Is cancer hereditary?

Only about 5% to 10% of cancers are caused by inherited gene changes, such as BRCA1 and BRCA2 or Lynch syndrome. A strong family history, with several relatives affected or cancer at a young age, may warrant genetic counseling and testing.

How can I reduce my risk of cancer?

Avoid tobacco, limit alcohol, keep a healthy weight, stay active, eat a fiber-rich diet with less processed meat, protect your skin from the sun, get HPV and hepatitis B vaccines, and attend recommended cancer screenings.