7.11.2: Risk Factors/Protective Factors
Risk factors for cancers vary widely. Specific biological factors can put a person at risk for developing cancer, such as previous infections or treatment with specific drugs or radiation therapy, hormonal influences, and inherited genetic factors. Some of the most common biological factors include (but are not limited to):
-
Specific genes (examples):
- Inherited mutations on either BRCA1 and BRCA2 genes can increase the risk of breast cancer by up to 72% and the risk of ovarian cancer by up to 44% (National Cancer Institute, 2020). See Figure 7.3 below.
- Mutation on the KRAS gene, which changes the proteins produced within the cell, causing it to grow uncontrollably (National Cancer Institute, 2022).
- Lynch syndrome, which is when a mismatch repair is inherited on one or more specific genes that increases the risk of colorectal cancer by 40-70% (Imyanitov et al., 2023).
Risk factors for cancers vary widely. Specific biological factors can put a person at risk for developing cancer, such as previous infections or treatment with specific drugs or radiation therapy, hormonal influences, and inherited genetic factors. Some of the most common biological factors include (but are not limited to):
-
Specific genes (examples):
- Inherited mutations on either BRCA1 and BRCA2 genes can increase the risk of breast cancer by up to 72% and the risk of ovarian cancer by up to 44% (National Cancer Institute, 2020). See Figure 7.3 below.
- Mutation on the KRAS gene, which changes the proteins produced within the cell, causing it to grow uncontrollably (National Cancer Institute, 2022).
- Lynch syndrome, which is when a mismatch repair is inherited on one or more specific genes that increases the risk of colorectal cancer by 40-70% (Imyanitov et al., 2023).
Several pathogens are also known to cause cancers. These include:
- Human Papillomavirus (HPV) is most known for its relation to cervical cancer, but it also increases the risk of cancers in both female and male reproductive systems, as well as head and neck cancers.
- Helicibactor pylori is indicated in stomach cancers and non-Hodgkin Lymphoma.
- Epstein-Barr virus increases the risk of Hodgkin and some non-Hodgkin Lymphomas, as well as nasopharyngeal cancer.
- Hepatitis B and C increase the risks for liver cancer and others (American Association for Cancer Research, 2023).
Epigenetic changes refer to alterations outside of DNA, which can cause changes to the way the cell functions, but may be reversible. Exposures to certain toxins can cause epigenetic changes which cause cancer (National Cancer Institute, 2022). Any substance that can cause mutations in cellular DNA is called a mutagen, and any substance that is known to cause those mutations that lead to cancer is called a carcinogen. Carcinogens are usually studied in lab animals and then confirmed with epidemiological studies. The International Agency for Research on Cancer (IARC, a division of the WHO) maintains lists of possible, probable, and known carcinogenic substances or environmental exposures as research identifies them. Three levels of carcinogenicity are described in their regular publications (called Monographs), outlining the scientific evidence for each hazardous exposure:
1. Carcinogenic to humans
2a. Probably carcinogenic
2b. Possibly carcinogenic
3. Not classifiable as to its carcinogenicity in humans
Additionally, the CDC, NIH, and FDA collaborate on the National Toxicology Program (NTP) and release updated lists of known or reasonably anticipated carcinogens every few years. However, just because someone is exposed to a particular carcinogen does not guarantee that they will get cancer. Some carcinogens are hazardous even at low doses or for a short period of time, while others affect humans after repeated exposures of long durations (American Cancer Society, 2019).
Probably one of the most well known carcinogens is tobacco smoke. Smoking is a factor in nearly 20% of all cancer cases - including lung cancer and 17 others. Exposure to tobacco smoke increases the risk of kidney and bladder cancer, leukemia, female reproductive cancers, cancers of the head and neck, and cancers of the digestive tract. Nearly 30% of all cancer deaths can be attributed to tobacco products as well (American Association for Cancer Research, 2023). Environmental exposures to radiation (including UV radiation and skin cancer), toxic chemicals (such as asbestos and lead), or pollutants (such as particulate matter in the air we breathe) are also a significant risk. Many jobs have high levels of exposures to carcinogens. Firefighters, for example, are exposed to high levels of toxins from burning plastics and synthetic materials. These exposures can increase their risk of several different types of cancers over their lifetime (American Association for Cancer Research, 2023).
About 20% of all cancers are also related to just 4 lifestyle behaviors: alcohol consumption, nutrition, physical activity, and weight management. Obesity - particularly abdominal (visceral) obesity, is associated with chronic inflammation, prediabetes, and changes in sex hormones - all of which can increase the risk of cancer. Overweight and obesity are linked to 15 different types of cancer, and may be to blame for the rise in colorectal cancer seen in young people (under 50 years old) in the past decade (American Association for Cancer Research, 2023). For an infographic on obesity and cancer, see Fig. \(\PageIndex{2}\) below.
Conversely, physical activity can decrease the risk of at least 9 cancers, with likely protection for more as well. It is estimated that over 46,000 cancer cases could be prevented if people engaged in the minimum physical activity guidelines of getting 150 minutes of moderate activity, plus 2 days of muscle strengthening exercises per week. Currently, less than ¼ of American adults meet this minimum (American Association for Cancer Research, 2023).