The study, published in The Lancet Respiratory Medicine, found that lung adenocarcinoma, the most common type of lung cancer in non-smokers, comprises nearly 60% of lung cancer cases in women, compared to 45% in men.
Adenocarcinoma is the most common lung cancer of all lung cancers, and it’s the most common lung cancer in the U.S. and a recent study has shown that it is more frequently diagnosed in non-smokers, especially women, than men, and is more common in younger individuals compared to other types of lung cancer. [1]
Genetics:
One of the biggest risks of lung cancer in non-smokers is genetic mutations, particularly in the EGFR gene. This gene helps control cell growth and division, any changes in the EGFR gene can potentially lead to cancer.
TP53 gene is the gene that helps prevent cancer by controlling cell growth. Certain mutations in this gene can also contribute to lung cancer and are more common in non-smoking women than in men. When TP53 mutates, cells can grow uncontrollably. The hormone estrogen has a relation with this gene mutation which increases the risk of lung cancer in women over time.[2]
Another important gene is KRAS. Mostly KRAS gene mutations are seen in smokers but recent studies have shown that they’re increasingly found in non-smokers, especially women.
Hormones:
Besides genetic factors, hormone changes in women might also affect tumor growth. Estrogen hormone receptors are present in the lung tissue of women, and research suggests estrogen can trigger tumor growth. However, studies show that women on hormone replacement therapy (HRT) have a lower risk of lung cancer compared to those not on HRT.
Chronic Inflammation:
Apart from genetics and hormones, chronic inflammation could also be a reason for increasing lung cancer in non-smoking women. Women are more prone to develop autoimmune diseases than men, and immune system problems can play a part in cancer. Constant inflammation can repeatedly damage tissues which further leads to DNA changes and might trigger abnormal cell growth, and in the end, it can raise the risk of cancer.
It’s not these factors: Recent studies suggest that exposure to tiny air particles, called PM2.5 (2.5 micrometers or smaller), can also cause these mutations in non-smoking women. Reports suggest that PM2.5 levels are rising in many areas. This could be a reason for the increased prevalence of lung cancer in non-smoker women. Women are exposed to air pollution differently. While men often encounter pollution from factory jobs, women are exposed more to indoor pollution from cooking and heating with materials like wood, coal and kerosene, which increases the risk.[2]
Women are biologically more prone than men to certain genetic mutations that increase the risk of lung cancer. However, factors like hormonal changes, immune system issues, increasing pollution, and longer life spans are making these risks even greater. Recent findings also suggest that HPV might also be linked to lung cancer in women. Anyways, more studies and preventive actions are crucial.
References:
1) Uysal-Onganer, Pinar. n.d. “Why Is There an Increase in Lung Cancer Among Women Who Have Never Smoked?” The Conversation. https://theconversation.com/why-is-there-an-increase-in-lung-cancer-among-women-who-have-never-smoked-249406.
2) Why are lung cancer rates rising in people who've never smoked?
(Input from various sources)
(Rehash/Dr.Noureen/SSK)