Lung cancer, primarily consisting of lung squamous cell carcinoma (LUSC) and lung adenocarcinoma (LUAD), is the leading cause of cancer deaths in the world(Bray, Ferlay, et al. 2018). In 2020, it is estimated that there were 2206,771 new lung cancer cases, with 1435943 in males and 770828 in females(Zhang, Vaccarella, et al. 2023). Lung cancer not only imposes a heavy burden on the physical and mental health of sufferers around the world but also creates a world economic burden(Choi and Ryu 2018, Liao, Shun, et al. 2014, Bencina, Chami, et al. 2023).
Currently, lung cancer is mostly detected at an advanced stage due to symptoms such as coughing, coughing up blood, difficulty breathing, and chest pains(Florian, Kocher, et al. 2015). Unfortunately, Lung cancer patients are usually asymptomatic in the early stages(Hoffman and Sanchez 2017). Chest X-rays and computed tomography scans are the most commonly used methods for diagnosing lung cancer(Wiener, Gould, et al. 2015, Doroudi, Pinsky, et al. 2018). However, since they can only detect visible, irreversible changes in the lung, more diagnostic methods are needed. To overcome this challenge, new specific biomarkers must be discovered.
In recent years, It has been gradually recognized that the Cellular complexity of the tumor microenvironment (TME) is importantly linked to cancer development, progression, and metastasis (Joyce and Pollard 2009). The TME infiltrates many different cell types, such as carcinoma cells, sarcoma cells, immune cells, endothelial cells, and fibroblasts(Arneth 2019). Immune cells are an important part of the immune system and can recognize and destroy occult cancer cells(Aranda, Chaba, et al. 2018). A study using tissue microarrays and immunohistochemistry to identify immune cells in non-small cell lung cancer (NSCLC) found that NSCLC tumors infiltrated with various types of T cells, B cells, macrophages, NK cells, and DCs(Banat, Tretyn, et al. 2015). In addition, many studies have found immune cells influence survival in NSCLC patients(Donnem, Hald, et al. 2015, Paulsen, Kilvaer, et al. 2015, Feng, Li, et al. 2016). Therefore, exploring immune cells associated with lung cancer development contributes to early screening and prevention of lung cancer. However, there is still a lack of systematic studies to assess the causal relationship between immune cells and lung cancer, and human causal inferences may be biased by confounders because exposure and outcome share a common cause in confounding. The unavoidable design weaknesses of conventional observational studies are because many putative risk factors, including smoking behavior(Aredo, Luo, et al. 2021), alcohol consumption(Freudenheim, Ritz, et al. 2005), and chemical environmental exposures(Zablotska, Lane, et al. 2013), are closely related to lung cancer. This can cause confounds in traditional studies.
MR uses hundreds of genetic variants as instrumental variables and can be used to identify biomarkers for disease-related traits(Burgess, Foley, et al. 2020, Mohammadi-Shemirani, Sjaarda, et al. 2019). It is less confusing because it relies on the random segregation of alleles at meiosis and random assignment at conception, thus breaking the link with almost all interfering elements(Richmond and Davey Smith 2022). Our study performed a framework of MR analysis to investigate the potential causal relationship between 731 immune cell traits and lung cancer.