Introduction
The cancer statistics of China and the United States in 2022 ranked the incidence and mortality rate of lung cancer patients [
1]. In the United States, the incidence of lung cancer is second only to breast cancer, and the mortality rate is first. Lung cancer has become one of the important causes of tumor-related death. From the pathological perspective, lung cancer can be roughly divided into non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC), among which NSCLC accounts for about 80–85%, including adenocarcinoma, squamous cell carcinoma, and other histological subtypes [
2]. Apar et al. [
3] reported that the 5-year survival rate of NSCLC was only 26.4%.
Tertiary lymphoid structures (TLSs) are named after the primary and secondary lymphatic organs (peripheral immune organs or peripheral lymphatic organs which includes the spleen, lymph nodes, pharyngeal tonsils, appendix, and lymph nodules and lymph tissue distributed throughout the body). Primary lymphatic organs mainly include the thymus and bone marrow. Secondary lymphatic organs include the spleen, lymph nodes, pharyngeal tonsils, appendix, and lymph nodules, as well as the lymph tissue distributed throughout the body. Lymphoid tissue associated with immunity, including mucosa-associated lymphoid tissue and skin-associated lymphoid tissue, is known as TLS. TLS is defined as an ectopic lymphaden-like structure in the tumor, which may be accompanied by germinal center formation, mainly including T cells, B cells, dendritic cells, and high endothelial vein [
4,
5]. The purpose of this study was to observe TLS formation in NSCLC tissues and analyze its relationship with clinicopathologic features and patient prognosis. To determine whether TLSs in the tumor microenvironment are beneficial or harmful to patients, analyzing their location, density, and maturity is necessary [
6].
Discussion
In malignant tumors, cancer cells maintain continuous cell growth by interacting with the host immune system and surrounding stromal cells. Immune checkpoint inhibitors are now part of standard therapy for advanced or recurrent NSCLC. Currently known predictors of NSCLC include programmed cell death ligand 1 expression in tumor tissue, tumor mutation burden, tumor-infiltrating lymphocytes, gut microbiota, and TLS [
9], which forms new opportunities for cancer therapy. TLS may be a new predictive biomarker for immune checkpoint blocking. TLS reflects the tissue aggregation of immune cells in non-lymphoid tissues formed after birth. Under normal physiological conditions, TLSs are not present in the body. They start appearing during chronic inflammation, such as autoimmune diseases, chronic infections, and cancer. In malignant tumors, mature TLSs induce antitumor responses [
10]. TLS-associated dendritic cells are key to establishing local T-cell-mediated antitumor responses by presenting tumor antigen peptides to T cells located in T cell TLS compartments [
11]. Successful binding between naïve CD8
+ T cells and antigen-presenting cells activates immature T cells into CD8
+ T cells with cytotoxic functions, which can kill intracellular pathogens and tumor cells. However, B cells in immature TLSs may produce inhibitory factors that inhibit immune cell function. Overall, TLSs have a bivalent influence on host–tumor interactions, and they are found in almost all solid tumors. Studies have shown that TLSs indicate a favorable prognosis for most human tumors, including breast cancer [
12], lung adenocarcinoma (LUAD) [
13], hepatocellular carcinoma [
14], colorectal cancer [
15], cutaneous squamous cell carcinoma [
16], gastric cancer [
17], cervical cancer [
18], and oral cancer [
19].
The significance of TLSs in lung tissue has raised concerns. Hong et al. used clinical data from 515 LUAD patients in a The Cancer Genome Atlas (TGCA) cohort to investigate the association between TLS markers and the immune microenvironment, tumor mutation burden, and driver gene mutations. They showed that LUAD patients with high TLS characteristics had good immune microenvironment and good prognosis [
11]. Karīna et al. used immunohistochemistry to show that TLS density was the most important independent prognostic marker in untreated LSCC patients, and its performance was superior to tumor stage [
20]. Mehrdad et al. quantified TLS in resected NSCLC whole-tumor tissue sections by considering the ‘absolute count’ of Agg and/or FOL [
21]. Only a few studies have examined TLS maturity in LUAD. Ren et al. found that TLS maturity was higher in patients with higher tumor stages [
22]. Wakasu et al. suggested that mature TLSs may support antitumor immunity through lymphocyte activation [
23].
This study examined the associations between TLS and OS, patient pathologic characteristics, and CD8 staining intensity. This study revealed that CTtotal and overall TLS in NSCLC tissue were independent prognostic factors for good patient prognosis, consistent with the results of previous studies [
21,
24]. However, most studies only examined TLS in tumor tissue according to density and location. To the best of our knowledge, this study is the first to identify immature CT TLSs [Agg (CT) and FOL-I (CT)] associations with clinicopathologic features and as independent prognostic factors associated with good prognosis and protective effect. These results are advantageous, because the area ratios of Agg (CT) and FOL-I (CT) in H&E sections are easier to quantitate than other indicators, and only the CT part requires investigation. A relatively large specimen tumor volume often cannot be retrieved completely in pathological sampling. The important role of indicators in the CT region in NSCLC can help patients with large tumor volume (especially advanced stage patients). TLS can be evaluated as a diagnostic H&E component and can be easily introduced as a relevant prognostic parameter in routine pathology.
Moreover, this study revealed that FOL-I (CT) (
P = 0.037) and overall TLS (
P = 0.037) were related to smoking status in NSCLC patients. Mathieu et al. investigated the mechanisms of tertiary lymphoid tissue (TLT) formation in the lungs of cigarette smoke-exposed mice [
25]. Cigarette smoke-induced pulmonary TLTs included T cells, B cells, dendritic cells, and macrophages. This finding suggests that lung inflammation caused by smoking contributes to TLS formation.
Considering the study sample, the limitations of this study include the low number of cases and the retrospective single-center evaluation. However, the sample included a large number of advanced patients, consistent with the main beneficiaries of this study. Further research is required in depth and exploit the underlying mechanism.
In conclusion, the presence of different TLS maturity and location provides new insights into prognosis for NSCLC patients. Immature CT TLS can be a crucial clinicopathological parameter.
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