How Smoking Can Lead To Cancer Development
Smoking remains one of the biggest causes of preventable deaths globally. According to the Centers for Disease Control and Prevention (CDC), smoking accounts for 1 in about five deaths in the United States every year.
As of 2019, 14% of the adult population in the country are smokers.
The American Lung Association states that there are more than 600 ingredients present in a cigarette. Each cigarette releases about 7000 chemicals when it is burnt. Out of these, close to 70 chemicals are proven carcinogens (cancer-causing substances). Some of them are:
When a person inhales cigarette smoke, these carcinogens and other chemicals reach the lungs and are distributed throughout the body.
Once these carcinogenic chemicals enter the body, they are detoxified by the cytochrome P450 group of enzymes (CYPs).
These CYP enzymes convert these carcinogens into a more active intermediary form called DNA adducts. DNA adducts are parts of the DNA that attach themself to these cancer-causing chemicals.
The intermediaries lead to DNA damage and abnormal cell multiplication and have to be quickly detoxified by other enzymatic processes. Unfortunately, in some people, the number of cancerous intermediaries builds up at a faster rate than they are eliminated. This leads to cancer.
There are other carcinogens in cigarette smoke that directly form DNA adducts without the help of the CYP enzymes. These lead to direct DNA damage and cell abnormalities, and resultant cancer.
Smoking – A Risk Factor for Breast Cancer
While smoking is a risk factor for all types of cancer, it is significantly associated with breast cancer in women.
In the United States, 1 in every eight women will be diagnosed with breast cancer in her lifetime. Smoking increases this risk drastically.
A study published in the BioMed Central Ltd forum analyzed the risk of breast cancer in women who smoked.
102,927 women were chosen and monitored for 7.7 years. In the end, 1815 women developed invasive breast cancer. The study found that smokers had a 14% higher risk of developing breast cancer than non-smokers.
Learn More: How Genes Influence Your Risk for Nicotine Dependence?
This study also mentions that women who start smoking before 17 had a significantly higher risk (24%) for breast cancer.
Another study analyzed the risk of breast cancer in 111,140 active smokers and 36,017 passive smokers (people who don’t smoke themselves but are exposed to other people’s cigarette smoke).
According to the study, some factors that increase the risk of breast cancer are:
- Smoking at a younger age
- Number of years of smoking
- Smoking before the first pregnancy
Does Secondhand Smoke Increase Breast Cancer Risk?
Secondhand smoke is also called passive smoking and is smoke that a person inhales unintentionally. For example, people can inhale tobacco smoke by just being around others who smoke. According to the California Air Resources Board, secondhand smoke is a proven carcinogen.
The smoke that is released from the burning ends of cigarettes is called sidestream smoke. Sidestream smoke is unfiltered and hence contains more harmful substances than the smoke that a smoker breathes out.
A 2013 study analyzed the risk of breast cancer in 322,988 active, passive, and non-smokers.
Compared to non-smoking women, those exposed to passive smoke at home or work had a higher risk of developing breast cancer.
How Does Genetics Influence Smoking And Breast Cancer Risk?
The GSTM1 Gene
The GSTM1 gene (glutathione S-transferase mu 1 gene) helps produce the glutathione S-transferase enzyme that belongs to the Mu class. The Mu class of enzymes helps in eliminating carcinogens and other environmental toxins from the body.
rs366631 is a single nucleotide polymorphism or SNP in the GSTM1 gene.
People with the GSTM1 null genotype have a higher risk of developing breast cancer when exposed to cigarette smoke.
Null genotype is the non-functional variant of the gene that results in total loss of function of the gene.
Here, the TT genotype is the null genotype.
The risk of breast cancer was also more severe in postmenopausal smokers with the GSTM1 null genotype.
| Genotype | Implication |
| TT | Increased risk of breast cancer upon smoking |
| CT | Normal risk of breast cancer upon smoking |
| CC | Normal risk of breast cancer upon smoking |
The SLC4A7 Gene
The SLC4A7 gene (Solute Carrier Family 4 Member 7 gene) helps produce a protein that transports sodium and bicarbonate ions. It also plays a role in the metabolism of different acids, ions, and amine compounds.
rs4973768 is an SNP in the SLC4A7 gene. A meta-analysis has reported an increased risk for breast cancer upon smoking in T allele carriers.
| Genotype | Implication |
| TT | Increased risk of breast cancer upon smoking |
| CT | Increased risk of breast cancer upon smoking |
| CC | Normal risk of breast cancer upon smoking |
Reducing Smoking to Lower Breast Cancer Risk
Get Help To Quit Smoking
There are so many government and private bodies that help people with tobacco addiction. You can get help from some of these rehab centers to stop or limit smoking. It takes time and effort to curb the craving. Here are some pointers that can help you with this.
- Take help from friends and family
- Keep yourself busy
- Take professional help if you are unable to quit on your own
- Consider de-addiction medications
Avoid Smoking Triggers
For people who have been smoking for years together, some places, smells, habits, or environments can create an urge to smoke. Understand these triggers and stay away from them. Practice the below activities to make quitting smoking easier.
- Throw away your cigarettes and lighters
- Keep your body hydrated
- Eat healthy food and stay away from caffeinated drinks and alcohol as they can increase the urge to smoke
Stay Away From Secondhand Smoking
Secondhand smoking ends up harmful to non-smokers. Here are ways you can limit/eliminate secondhand smoke exposure.
- Stand a few feet away from smokers.
- Do not allow people to smoke inside your house or in closed workspaces.
- Restrict people from smoking in your car.
- Avoid visiting restaurants, pubs, and bars that put smokers and non-smokers in the same space.
Get Genetic Testing Done
Genetic testing helps identify genetic factors that could increase your breast cancer risk. If you do have a high genetic risk, regular screening may help.
Summary
- Smoking is one of the major causes of preventable deaths globally. Smoking leads to a variety of health problems, including cancers.
- The chemicals in cigarette smoke can alter DNA and encourage the formation of DNA adducts. This leads to abnormal cell division and growth, causing cancer.
- Women who start smoking at a younger age, have increased lifetime exposure to smoking, or smoke excessively before the first pregnancy are more likely to develop breast cancer.
- Secondhand smoking or passive smoking also increases a woman’s risk of developing breast cancer.
- Changes in the GSTM1 and SLC4A7 genes can both increase a woman’s risk of developing breast cancer due to smoking.
- Getting help to quit smoking, staying away from triggers, and protecting oneself from secondhand smoke can all bring down the effect of smoking on breast cancer.
- Opting for genetic testing will tell if a woman is at a higher risk of developing breast cancer because of smoking. If so, taking help to limit/quit smoking and getting screened for cancer regularly help.
References
- https://pubmed.ncbi.nlm.nih.gov/16172223/
- https://www.webmd.com/breast-cancer/news/20050311/secondhand-smoke-linked-to-breast-cancer
- https://www.cdc.gov/tobacco/campaign/tips/diseases/cancer.html
- https://pubmed.ncbi.nlm.nih.gov/2404408/
- https://smokefree.gov/quit-smoking/getting-started/steps-to-manage-quit-day
- https://www.cdc.gov/tobacco/campaign/tips/quit-smoking/index.html
- https://onlinelibrary.wiley.com/doi/full/10.1002/ijc.28508
- https://www.frontiersin.org/articles/10.3389/fonc.2019.00044/fullhttps://pubmed.ncbi.nlm.nih.gov/33913154/
