Lung Tumours Conti...

## Summary This section provides a comprehensive overview of primary lung tumours, focusing on carcinomas as the most prevalent type. It details the aetiology, pathogenesis, and molecular aspects of lung cancer, including the significant impact of smoking and other environmental factors. The morphology of major histological subtypes like adenocarcinoma, squamous cell carcinoma, large cell carcinoma, and small cell lung carcinoma is described, alongside their respective precursor lesions and characteristic genetic mutations. The comparison between small cell lung carcinoma (SCLC) and non-small cell lung carcinoma (NSCL C) highlights their distinct clinical behaviours and treatment implications. The section also covers the spread patterns, clinical manifestations, paraneoplastic syndromes, and treatment strategies for lung tumours, emphasizing the advent of targeted therapies and immune checkpoint inhibitors. Additionally, it discusses carcinoid tumours, a less common but distinct group of neuroendocrine neoplasms originating in the lungs. ## Key Points - **~95% of primary lung tumours are carcinomas**, with the remaining 5% comprising carcinoids, mesenchymal malignancies, lymphomas, and benign lesions. - **Hamartoma** is the most common benign lung tumour, appearing as a discrete "coin lesion" on imaging. - **Carcinoma of the lung** is the leading cause of cancer-related deaths in industrialized countries, with peak incidence in the fifties and sixties. - **Four Major Histologic Types** of lung carcinoma are Adenocarcinoma, Squamous cell carcinoma, Small cell carcinoma, and Large cell carcinoma. - **Smoking** is the most important aetiological factor, accounting for ~90% of lung cancers. - **Asbestos exposure** synergizes with tobacco smoke, significantly increasing lung cancer risk. - **Key Targetable Mutations** in lung adenocarcinomas include EGFR, KRAS, and ALK rearrangements, driving personalized treatment approaches. - **Small Cell Lung Carcinoma (SCLC)** is highly aggressive, virtually always metastatic at diagnosis, and treated with systemic chemotherapy. - **Non-Small Cell Lung Carcinoma (NSCLC)** is more likely to be resectable and may respond to targeted therapies. - **Carcinoid Tumours** are low-grade neuroendocrine carcinomas, often resectable and curable, with typical and atypical subtypes. - **Pleural lesions** include effusions (transudates and exudates), pneumothorax, haemothorax, chylothorax, and malignant mesothelioma. - **Malignant Mesothelioma** is a rare cancer of mesothelial cells, strongly linked to asbestos exposure with a long latent period. - **Upper Respiratory Tract Lesions** encompass acute infections (pharyngitis, epiglottitis, laryngitis) and neoplasms like nasopharyngeal carcinoma, laryngeal papilloma, and carcinoma of the larynx. - **Carcinoma of the Larynx** is predominantly squamous cell carcinoma, with glottic tumours having a better prognosis due to early symptoms and less lymphatic spread. ## Detailed Notes ### Overview of Primary Lung Tumours - **~95%** of primary lung tumours are carcinomas. - The remaining 5% consist of carcinoids, mesenchymal malignancies (fibrosarcomas, leiomyomas), lymphomas, and benign lesions. - The **most common benign tumour** is **Hamartoma**. It is typically spherical, small (1–4 cm), and appears as a discrete "coin lesion" on imaging. It is composed mainly of mature cartilage admixed with fat, fibrous tissue, and blood vessels. Clonal cytogenetic abnormalities have been confirmed, technically classifying it as a benign neoplasm rather than a true hamartoma. ### Carcinoma of the Lung - **Most important cause of cancer-related deaths** in industrialised countries. - Leading cause of cancer deaths in both men and women. - Estimated ~221,200 new cases and 158,040 deaths in the USA (2016 figures). - Peak incidence occurs in the **fifties and sixties**. - At diagnosis, >50% of patients already have distant metastases, and an additional 25% have regional lymph node disease. - The **overall 5-year survival is approximately 16%**, a figure that has not changed significantly over 35 years. - Even with disease localised to the lung, the 5-year survival is only 45%. **Four Major Histologic Types:** | Type | Key Features | | :---------------------- | :------------------------------------------------------------------------------- | | Adenocarcinoma | Most common overall; most common in women, non-smokers, and those <45 years old. | | Squamous cell carcinoma | Strong smoking association; typically central location. | | Small cell carcinoma | Strongest smoking association; neuroendocrine in nature; almost always metastatic at diagnosis. | | Large cell carcinoma | Undifferentiated; diagnosis of exclusion. | - The historical division between **SCLC (Small Cell Lung Carcinoma)** a