Lung cancer remains the leading killer With approximately 2.3 million new cases and 1.8 million deaths annually worldwide, lung cancer causes more deaths than breast, colon, and prostate cancer combined. Despite advances in targeted therapy and immunotherapy, the 5-year survival rate for advanced disease remains below 10%, underscoring the critical need for deeper biological understanding.
Two major categories Lung cancer divides into small-cell lung cancer (SCLC, 12% of cases) - aggressive and prone to early distant metastasis - and non-small-cell lung cancer (NSCLC, 80-85%). Within NSCLC, adenocarcinoma (LUAD, 45% of all lung cancers) and squamous cell carcinoma (LUSC, 21%) are the dominant histologic subtypes with distinct molecular profiles and treatment approaches.
Racial and ethnic disparities are profound Lung cancer incidence, molecular mutation profiles, and outcomes differ substantially by race and ethnicity. Individuals with African ancestry (AA) have higher mortality rates and earlier age of onset than those with European ancestry. Asian populations show higher EGFR mutation rates but longer survival. Native Americans have the highest incidence rates, linked to historic smoking prevalence in certain states.
Review scope This comprehensive review from the University of South Alabama covers the full biological roadmap: epidemiology and risk factors by race, molecular progression steps, nuclear and mitochondrial genetic alterations, epigenetics, microbiome roles, immune system changes, detection methods, and treatment strategies for both NSCLC and SCLC.
Smoking is the primary but not sole risk factor Cigarette smoking drives most lung cancer cases, but 10-25% of lung cancer patients have never smoked. In countries like Morocco, 75% of women with lung cancer were never-smokers. This underscores that non-smoking risk factors - radon exposure, air pollution (PM2.5, NO2), occupational carcinogens, cooking fumes, and dietary factors - are critical, especially in populations where tobacco use is lower.
Racial disparities in incidence Non-Hispanic African American males have the highest lung cancer incidence and mortality rates of any racial-ethnic group in the U.S. Despite lower cigarette consumption, they develop lung cancer at higher rates than European Americans, in part due to differences in nicotine metabolism (lower cotinine glucuronidation) and disparities in screening access and quality of care. Native Americans in some states experience mortality rates two to three times higher than most Western states.
Gender trends are shifting Historically more common in men, lung cancer incidence is now higher in young women under age 50 than in men of the same age, notably among non-Hispanic White and Asian/Pacific Islander populations. Passive smoke exposure at home accounts for approximately 18% of lung cancer cases among never-smoking women. Female lung cancer trends reflect historical smoking patterns with a time lag.
Dietary and environmental contributors Elevated PM2.5 and NO2 air pollution significantly increases lung cancer risk. Arsenic in drinking water is a 'convincing' risk factor per WHO. Higher fruit and vegetable intake is protective. Higher processed meat, alcohol, and dietary fat intake are associated with increased risk. These risk factor distributions vary substantially across racial and ethnic groups, contributing to observed outcome disparities.
NSCLC molecular progression NSCLC develops through a stepwise molecular process: normal epithelium progresses to hyperplasia, then metaplasia, dysplasia, carcinoma in situ, and finally invasive carcinoma. Each step involves accumulating genetic alterations including driver mutations, epigenetic changes, and non-coding RNA dysregulation that progressively disrupt cell growth control and tissue invasion barriers.
LUAD vs. LUSC mutation profiles LUAD (adenocarcinoma) is driven primarily by EGFR mutations (especially in never-smokers), KRAS mutations (in smokers), and ALK/ROS1/RET fusions. LUSC (squamous cell carcinoma) is predominantly associated with TP53 mutations, KEAP1, PIK3CA, and NFE2L2 alterations - reflecting smoking-induced mutagenesis. These distinct mutation landscapes explain why targeted therapies (EGFR TKIs, ALK inhibitors) work in LUAD but have fewer targets in LUSC.
Racial variation in mutation profiles Asian populations have significantly higher EGFR mutation frequencies than European or African Americans, and better outcomes partly because EGFR-mutated tumors respond to targeted TKI therapy. African Americans with LUAD show higher rates of PTPRT and JAK2 mutations. European Americans with LUSC have higher TP53, PIK3CA, KEAP1, and NFE2L2 mutation frequencies than Japanese patients. These population-specific genomic differences require race-stratified treatment considerations.
Mitochondrial and epigenetic alterations Beyond nuclear DNA, mitochondrial DNA mutations, epigenetic reprogramming (DNA methylation, histone modification, non-coding RNA changes), and microbiome dysbiosis contribute to lung cancer development. Epigenetic silencing of tumor suppressor genes through promoter methylation is particularly important in lung cancer, and some epigenetic markers vary by ancestral background - adding another layer to racial disparity in cancer biology.
Tumor immune microenvironment The lung tumor immune microenvironment involves complex interactions between cytotoxic CD8+ T cells (anti-tumor), regulatory T cells and M2 macrophages (immunosuppressive), PD-1/PD-L1 checkpoint signaling, and natural killer cells. High CD8+ T-cell infiltration is associated with better immunotherapy response, while an immunosuppressive microenvironment predicts resistance.
Immune checkpoint pathways ICIs blocking PD-1/PD-L1 or CTLA-4 achieve objective response rates of approximately 42% in NSCLC patients, and over 50% in those with PD-L1 expression at least 50%. ICIs now form the backbone of first-line NSCLC treatment for non-oncogene-addicted advanced disease, either alone or combined with chemotherapy. Perioperative immunotherapy in stages II-III resectable NSCLC has reduced postoperative recurrence and improved overall survival.
Microbiome dysbiosis in lung cancer Emerging evidence implicates disruption of the lung and gut microbiome communities (dysbiosis) in lung cancer development and in modulating immune responses to treatment. Specific bacterial species in the lung microbiome correlate with tumor immune composition and ICI response. Gut microbiome composition influences systemic immunity and may modulate immunotherapy outcomes through the gut-lung immune axis.
Racial differences in immune biology Racial differences in lung cancer outcomes are not explained solely by mutation profiles or smoking exposure. Immune response patterns, cytokine profiles, and microbiome compositions also vary by ancestral background. Understanding these immune and microbial contributions to racial disparities may reveal new opportunities for more equitable and effective treatment approaches.
Surgery and radiotherapy Early-stage NSCLC (stages I-III) is treated with curative-intent surgery (wedge resection, lobectomy, pneumonectomy, sleeve resection) or stereotactic body radiotherapy for inoperable patients. Multi-modality approaches combining surgery with chemotherapy and/or radiation improve local and distant control in stages II-III but increase toxicity. Treatment choice depends on tumor stage, patient fitness, and pulmonary reserve.
Targeted therapies EGFR tyrosine kinase inhibitors (TKIs) are the standard first-line treatment for EGFR-mutated NSCLC, with first-, second-, and third-generation agents now available. ALK, ROS1, RET, BRAF, MET, and NTRK inhibitors target other molecular subsets. The KRAS G12C inhibitor sotorasib targets one of the most common KRAS mutations. These targeted agents have transformed NSCLC into a precision oncology paradigm for oncogene-addicted cases.
Immunotherapy advances PD-1/PD-L1 inhibitors are now standard across NSCLC lines - from neoadjuvant and adjuvant perioperative settings through advanced disease. CTLA-4 inhibitors combined with PD-1 blockade (e.g., nivolumab + ipilimumab) provide durable responses in some patients. Both smokers and non-smokers benefit from immunotherapy. SCLC treatments include chemotherapy (standard), etoposide-based regimens, and immunotherapy agents like atezolizumab and durvalumab.
Emerging technologies CRISPR-Cas9 technology is being explored for lung cancer biomarker identification and precision diagnostics, though clinical application remains early-stage. Nanoparticle drug delivery systems targeting NSCLC biomarkers are in development. Liquid biopsy (circulating tumor DNA, ctDNA) is increasingly used for mutation detection, treatment monitoring, and minimal residual disease assessment.
Multi-level causes of disparities Racial and ethnic disparities in lung cancer outcomes arise from multiple intersecting factors: differential access to low-dose CT screening, underrepresentation in clinical trials (limiting generalizability of treatment data), socioeconomic barriers to treatment, genetic ancestry-linked differences in molecular tumor biology, variation in tobacco metabolism, and provider-level implicit biases in treatment recommendations.
Genomics of disparity African American patients with LUSC show more genomic instability and aggressive molecular traits. Despite this, AA and Asian NSCLC patients demonstrate better outcomes than European Americans for same-stage cancer - likely due to different molecular subtypes (higher EGFR mutation rates in Asians enabling targeted therapy) rather than superior biology. Understanding population-specific molecular drivers is essential for equity in precision medicine.
Screening access disparities LDCT lung cancer screening in high-risk populations reduces mortality by approximately 20%, yet screening uptake is substantially lower in racial minority groups due to lack of awareness, reduced access to pulmonology specialty care, and historical exclusion from the trials that defined screening criteria. Expanding screening eligibility and community-based outreach to under-screened populations is a public health priority.
Future research directions Population-specific genomic databases, clinical trials with mandated racial diversity, and race-stratified biomarker analyses are needed. Integration of social determinants of health, microbiome profiling, epigenomic analyses, and AI-driven multi-omic modeling offer pathways to discovering the biological mechanisms behind racial disparities and developing more equitable diagnostic and therapeutic approaches.