The development of reliable gene expression profiling technology is having an increasing impact on our understanding of lung cancer biology. Our study aimed to determine any correlation between the phenotypic heterogeneity and genetic diversity of lung cancer. Microarray analysis was performed on a set of 46 tumor samples and 45 paired nontumor samples of nonsmall cell lung cancer (NSCLC) samples to establish gene signatures in primary adenocarcinomas and squamous-cell carcinomas, determine differentially expressed gene sequences at different stages of the disease and identify sequences with biological significance for tumor progression. After the microarray analysis, the expression level of 92 selected genes was validated by qPCR and the robust Bonferroni test in an independent set of 70 samples composed of 48 tumor samples and 22 nontumor samples. Gene sequences were differentially expressed as a function of tumor type, stage and differentiation grade. High upregulation was observed for KRT15 and PKP1, which may be good markers to distinguish squamous-cell carcinoma samples. High downregulation was observed for DSG3 in stage IA adenocarcinomas.Lung cancer is the leading cause of cancer death in the United States 1 and worldwide. The two major forms of lung cancer are nonsmall cell lung cancer (NSCLC %85% of all lung cancers) and small-cell lung cancer (SCLC %15%). NSCLC can be divided into three major histological subtypes: squamous-cell carcinoma, adenocarcinoma and large-cell lung cancer. Smoking causes all types of lung cancer but is most strongly linked with SCLC and squamous-cell carcinoma, while adenocarcinoma is the most frequent type in patients who have never smoked.2-5 Patients with early-stage NSCLC who undergo curative resection still have a substantial risk of developing metastases. The 5-year survival rates for patients with Stage IA and IB NSCLC are only 67 and 57%, respectively.

After several decades without maintained responses or long-term survival of patients with lung cancer, novel therapies have emerged as a hopeful milestone in this research field. The appearance of immunotherapy, especially immune checkpoint inhibitors, has improved both the overall survival and quality of life of patients, many of whom are diagnosed late when classical treatments are ineffective. Despite these unprecedented results, a high percentage of patients do not respond initially to treatment or relapse after a period of response. This is due to resistance mechanisms, which require understanding in order to prevent them and develop strategies to overcome them and increase the number of patients who can benefit from immunotherapy. This review highlights the current knowledge of the mechanisms and their involvement in resistance to immunotherapy in lung cancer, such as aberrations in tumor neoantigen burden, effector T-cell infiltration in the tumor microenvironment (TME), epigenetic modulation, the transcriptional signature, signaling pathways, T-cell exhaustion, and the microbiome. Further research dissecting intratumor and host heterogeneity is necessary to provide answers regarding the immunotherapy response and develop more effective treatments for lung cancer.

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Staining for these proteins marked intercellular junctions that are characteristic of stratified squamous epithelium and of neoplasias with this type of differentiation, and can be useful in the diagnosis of patients with squamous cell carcinoma of the lung. The high specificity of membrane staining for PKP1 and DSG3 and high sensitivity of cytoplasmic and membrane staining for KRT15 for the diagnosis of squamous cell carcinoma may be useful for the differential diagnosis of non-small-cell carcinomas.