Causes of Cancer: Infectious Agents

Question 1

attributable fraction

Answer 1

proportion of incidents that are likely to be caused by a risk factor

Question 2

attributable fraction for infectious agents

Answer 2

• uk less than 5%
• some countries over 40% (southeast africa)

Question 3

risk based on richness of country

Answer 3

• less developed regions = at least 25%
• more developed = at least 10%

Question 4

total number of cases a year due to infectious agents

Answer 4

2.2 million

Question 5

most common infections causing cancer

Answer 5

• H pylori
• HPV
• Hep b/c
• EBV
• schistosoma haematobium
• liver flukes

Question 6

liver flukes and cancer

Answer 6

• cause bile duct cancer
• causes chronic inflammation, which causes higher rates of proliferation and DNA damage
• bile duct cancer very common in china, thailand and south korea, less common in uk, europe
• corresponds with levels of liver fluke infections

Question 7

liver fluke infection cause

Answer 7

• eating fish that have been infected by the parasite
• can stay in host for many years

Question 8

H. Pylori and cancer

Answer 8

• gastric cancer
• 80-90% attributable fraction for some types
• bacterium damages mucous cells, and causes inflammation and immune response
• stomach ulcers also form
• more proliferation, causes more mutations

Question 9

viruses and cancer

Answer 9

HPV- cervix (100%), head and neck (50%)
Hep B- liver (80%)
EBV- pharynx (50%), hodgkins disease (30%)

Question 10

HPV and cancer

Answer 10

• many strains (200)
• most harmless- LOW RISK
• some associated with cancer- HIGH RISK (16, 18, 31)
• cervix, head and neck, penile, vulva and anus

Question 11

HPV causing cancer

Answer 11

• 8000 bp DNA
• viral E6 and E7 encode oncoproteins
• E6 binds to p53, which targets it for degradation
• prevents cell cycle arrest/apoptosis functions of p53
• E7 binds to Rb1, which targets it for degradation
• prevents Rb1 holding of E2F, so E2F free to promote cell cycle progression

Question 12

retroviruses in cancer

Answer 12

• HIV- kaposis sarcoma
• HTLV- T cell leukaemia (3% of people infected develop T-cell leukeamia) common in Japan, Caribbean, US, Italy, Africa
• insertion of cDNA is where problems happen (blocking TSGs and promoting oncogenes)