HSCI 2211 Risk factors

Mutagen

Anything that causes DNA damage.

Carcinogen

Anything that can cause cancer.

3 classes of mutagens

Chemicals, radiation, and infectious agents.

4 classes of carcinogens

Chemicals, radiation, infectious agents, and hereditary mutations.

Genetic instabilities

When genetic defence mechanisms do not work, causing mutations that can lead to cancer.

Hallmarks of cancer

Self-sufficiency in growth signals, insensitivity to antigrowth signals, evasion of apoptosis, limitless replicative potential, sustained angiogenesis, tissue invasion, and metastasis.

Risk factor

Any variable that increases the risk of cancer.

Main chemical risk factors for cancer

Tobacco and diet.

Dietary risk factors for cancer

Heavily processed foods, low fibre, and high calorie intake.

Cancer risk associated with tobacco

About 30%.

Cancer risk associated with diet

About 30%.

Cancer risk associated with infections

About 15%.

Cancer risk associated with genetics

About 7%.

Genes involved in genetic cancer risk

Tumour suppressor genes and oncogenes.

DNA adduct

A segment of DNA chemically bonded to a cancer-causing substance.

How can chemicals act as carcinogens?

They can bind to or break DNA, causing mutations.

What makes a chemical more carcinogenic?

Chemicals that bind to DNA more easily tend to be more carcinogenic.

What determines the probability of carcinogenesis?

Dose, potency, and duration of exposure.

Biological gradient / dose-response

Higher exposure to a factor leads to a greater magnitude or frequency of an effect.

What is the most potent carcinogenic chemical?

Aflatoxin.

Can be produced by certain molds

Tobacco and lung cancer

There is a clear correlation between cigarette exposure and lung cancer mortality.

Synergistic effects

Two or more factors work together to create an outcome greater than the sum of their separate effects.

Relative risk

A ratio comparing the chance of an event happening in one group to the chance of it happening in another group.

Relative risk of cancer in smokers

About 15–30× higher than nonsmokers.

Cancers with the highest relative risk in smokers

Lung, head and neck, esophageal, pancreatic, and bladder cancers.

#1 cancer causing commercial substance

Tobacco.

#2 cancer causing commercial substance

Asbestos.

Carcinogens in food

Ultra-processed foods, red meat, and excess calories leading to obesity.

Ultra-processed food carcinogens

Preservatives, emulsifiers, colour, and saturated fats.

Anti-carcinogens in food

Fresh fruits, vegetables, and high-fibre foods.

Cancers most significantly associated with obesity

Stomach, colon, and breast cancers.

Most common cancers among Canadian men

Prostate, lung, colorectal

Most common cancers among Canadian women

Breast, lung, colorectal

Major risk factors for common cancers

Age, smoking, and lifestyle factors such as obesity and poor diet.

How do infectious agents increase cancer risk?

By triggering chronic inflammation, altering cell-growth genes, or weakening the immune system.

Infections causing the most cancers

HPV, Hepatitis B, Hepatitis C, and Epstein-Barr virus (EBV), in that order.

Human Papillomavirus (HPV)

A viral infection strongly associated with cervical cancer.

Proportion of cervical cancers attributed to HPV

About 90%.

High-risk HPV genotypes responsible for ~75% of cervical cancers

HPV 16, HPV 18, and HPV 45.

Which high-risk HPV genotype causes the most cervical cancers?

HPV 16, which accounts for more than half.

Smoking and HPV

Smoking and HPV have a synergistic relationship that increases cervical cancer risk.

Alcohol

Greatly increases relative risk of head and neck cancers

What are the two natural sources of ionizing radiation?

1. Radon gas

2. Cosmic radiaiton

What are the two artificial sources of ionizing radiation?

1. Medical imaging (X-rays, CT scans)

2. Nuclear medicine / medical procedures