Epidemiology of Cancer

Definition and Burden of Cancer

• Cancer is a generic term for a group of over 100 diseases characterized by uncontrolled cell division and invasion of other tissues.
• Cancer results from genetic changes (mutation) in a cell, causing tumor cells to behave differently from normal cells.
• In 2020, there were 19.3 million new cancer cases and 10 million cancer deaths globally.
• By 2030, it is projected that there will be approximately 26 million new cancer cases and 17 million cancer deaths per year.
• 56% of new cancer cases occur in developing countries, and 64% of cancer deaths occur in developing countries.
• Breast cancer was the most commonly diagnosed cancer, followed by lung, colorectal, prostate, and stomach cancer.

Distribution of Cancer

• Age distribution: The incidence rate of cancer increases steadily with age, with a median age of diagnosis of 66 years.
• It kills more children (3-14 times) than any other disease.
• Sex distribution:
  • Higher incidence in men than in women, largely due to past exposure to tobacco smoking, alcohol consumption, and hazardous occupations.
  • Thyroid and gallbladder cancers are more common in women, related to diet, overweight, and estrogen.
• Geographical distribution:
  • Higher in industrialized sectors and nations.
  • Etiologic factors present in the biological, chemical, physical, or social environment contribute to the development of cancer.
• Socioeconomic status (SES):
  • People with lower SES have disproportionately higher cancer death rates than those with higher SES, regardless of demographic factors.

Factors Contributing to Cancer

• Biological agents:
  • Parasites (e.g., schistosoma haematobium, liver flukes) associated with bladder cancer and cholangio-cellular carcinoma.
  • Viruses (e.g., Hepatitis B, Epstein-Barr virus, Herpes virus) associated with liver cancer, Burkett's lymphoma, and cervical cancer.
• Chemical agents:
  • Asbestos, benzene, benzidin, mustard gas, and pesticides.
• Pharmaceuticals:
  • Post-menopausal hormonal therapy.
• Obesity:
  • Increases the risk of endometrial cancer, and probably increases the risk of breast, colon, and gallbladder cancer.
• Physical activity:
  • Reduces the risk of bladder, breast, endometrial, esophageal, kidney, and stomach cancer.
• Diet:
  • High correlation between dietary fat and colorectal, breast, endometrial, prostate, lung, and pancreatic cancers.
  • Salt-preserved diet and contaminated food increase the risk of stomach and nasopharyngeal cancer.
  • Diet rich in vegetables and fruits decreases the risk of many cancers.

Cancer Theory and Control

• 1/3 of cancers are preventable, 1/3 are curable if detected early, and 1/3 are palliative to improve quality of life.
• Aim of cancer control: Reduce cancer incidence, morbidity, and mortality through prevention, early diagnosis, treatment, and palliative care.
• Prevention:
  • Primary prevention:
    • Healthy diet
    • No smoking
    • No alcohol
    • Exercise/maintain optimal weight
    • Avoid radiation
  • Prophylactic surgery (e.g., breast, colorectal, cervical cancer)
  • Chemoprevention (e.g., tamoxifen for breast cancer, finasteride for prostate cancer)

Cancer Detection and Treatment

• Secondary prevention:
  • Early detection of cases after symptoms have developed (through community education)
  • Early detection in asymptomatic populations through mass screening programs (e.g., mammography, Pap test)
• Tertiary prevention:
  • Treatment of known cases by surgery, radiation, and chemotherapy or combination
  • Pain-relieving palliative treatment