What Are Lung Neoplasms?

Lung neoplasms are abnormal tissue growths originating in the lungs, encompassing both malignant tumors and a smaller category of benign neoplasms. The term is broader than "lung cancer," which refers specifically to malignant lesions; lung neoplasms as a class include carcinomas, carcinoid tumors, lymphomas arising in pulmonary tissue, sarcomas, and benign entities such as hamartomas, adenomas, and sclerosing pneumocytomas. In clinical medicine, pathology, and biomedical research, this taxonomy provides the framework for diagnosis, epidemiological classification, and treatment planning, and it underpins the coding systems used in health informatics and clinical data aggregation.

The pathological classification of lung neoplasms follows frameworks established by the World Health Organization (WHO), which has undergone significant revision as molecular and genetic characterization has become routine. The 2015 and 2021 WHO editions shifted classification from purely morphological criteria toward integrated morphological, immunohistochemical, and molecular profiles, reflecting the clinical relevance of driver mutations for targeted treatment selection.

WHO Classification of Lung Tumors

The WHO classification system organizes lung neoplasms into epithelial tumors (the largest category), mesenchymal tumors, lymphohistiocytic tumors, tumors of ectopic origin, and metastatic tumors. Within epithelial tumors, the major malignant entities are non-small cell carcinomas (adenocarcinoma, squamous cell carcinoma, large cell carcinoma, and adenosquamous carcinoma), small cell carcinoma, and large cell neuroendocrine carcinoma. Pre-invasive lesions, including adenocarcinoma in situ and squamous cell carcinoma in situ, occupy a distinct category with uncertain malignant potential. A detailed analysis of the 2021 WHO classification of lung tumors, published in the Journal of Thoracic Oncology, describes how advances in molecular pathology since 2015 reshaped the classification framework. Behavior codes in the WHO system distinguish benign tumors (/0), those of borderline behavior (/1), carcinoma in situ (/2), and malignant tumors (/3).

Benign Lung Neoplasms

Benign lung neoplasms are far less common than malignant ones and are often discovered incidentally on imaging performed for other reasons. Pulmonary hamartoma is the most common benign lung neoplasm in adults; it consists of a disordered mixture of normal lung tissue components, including cartilage, fat, and epithelium, and typically presents as a solitary pulmonary nodule with a characteristic "popcorn" calcification pattern on CT. Sclerosing pneumocytoma (formerly sclerosing hemangioma) is a benign epithelial tumor with complex histology that may mimic malignancy on imaging. Bronchial carcinoid tumors, though classified separately as neuroendocrine neoplasms, have low-grade malignant potential and are often included in discussions of lung neoplasms with more favorable prognoses. Distinguishing benign from malignant pulmonary nodules is a central challenge in thoracic radiology and drives significant investment in AI-assisted imaging tools.

Molecular Profiling and Neoplasm Characterization

The characterization of lung neoplasms has increasingly relied on molecular profiling. Somatic driver mutations in EGFR, KRAS, ALK, ROS1, BRAF, MET, and RET genes occur in defined subsets of lung adenocarcinoma and guide the use of targeted kinase inhibitors. PD-L1 expression levels on tumor cells and tumor-infiltrating immune cells predict response to checkpoint immunotherapy. High-throughput sequencing panels applied to surgical specimens or small biopsy samples can simultaneously identify mutations, copy number alterations, and gene fusions across dozens of clinically actionable loci. The Pathology Outlines WHO lung tumor classification reference provides a practical summary of the diagnostic criteria and immunohistochemical markers used to assign tumor types. The NCBI Bookshelf entry on small cell lung cancer covers the pathological and clinical features of this aggressive neuroendocrine neoplasm.

Applications

Research on lung neoplasms has applications in a wide range of clinical and engineering domains, including:

• CT and PET/CT imaging for pulmonary nodule detection and characterization
• AI-assisted classification of biopsy specimens and radiology images
• Biomarker assays and liquid biopsy platforms for driver mutation detection
• Cancer registry informatics and epidemiological database coding
• Radiation treatment planning systems for thoracic tumors