Editing Lung cancer (section)

===Classification===
[[File:Lung cancer histology collection.png|thumb|upright=1.4|alt=Microscope images of lung tissue. At top-left, healthy lung with clear air-filled alveoli. Others are full of tumor or material, per caption.|[[H&E stain]]ed samples from lung biopsies: (Top-left) Normal bronchiole surrounded by alveoli, (top-right) adenocarcinoma with papillary (finger-like) growth, (bottom-left) alveoli filled with mucin suggesting adenocarcinoma nearby, (bottom-right) squamous-cell carcinoma, with alveoli full of keratin.]]
[[File:Histopathology of small cell carcinoma, annotated.png|thumb|230px|Histopathology of small-cell carcinoma, with typical findings<ref>Image by Mikael Häggström, MD. Source for findings: {{cite web|url=https://www.pathologyoutlines.com/topic/lungtumorsmallcell.html|title=Lung - Small cell carcinoma|website=Pathology Outlines|author=Caroline I.M. Underwood, M.D., Carolyn Glass, M.D., Ph.D.}} Last author update: 20 September 2022</ref>]]
At diagnosis, lung cancer is classified based on the type of cells the tumor is derived from; tumors derived from different cells progress and respond to treatment differently. There are two main types of lung cancer, categorized by the size and appearance of the malignant cells seen by a [[histopathology|histopathologist]] under a [[microscope]]: [[small cell lung cancer]] (SCLC; 15% of cases) and [[non-small-cell lung cancer]] (NSCLC; 85% of cases).{{sfn|Thai|Solomon|Sequist|Gainor|2021|loc="Histology"}} SCLC tumors are often found near the center of the lungs, in the major airways.{{sfn|Rudin|Brambilla|Faivre-Finn|Sage|2021|loc="Signs and Symptoms"}} Their cells appear small with ill-defined boundaries, not much [[cytoplasm]], many [[mitochondria]], and have distinctive [[cell nucleus|nuclei]] with granular-looking [[chromatin]] and no visible [[nucleoli]].{{sfn|Horn|Iams|2022|loc="Pathology"}} NSCLCs comprise a group of three cancer types: [[adenocarcinoma of the lung|adenocarcinoma]],  [[squamous-cell lung carcinoma|squamous-cell carcinoma]], and [[large-cell lung carcinoma|large-cell carcinoma]].{{sfn|Horn|Iams|2022|loc="Pathology"}} Nearly 40% of lung cancers are adenocarcinomas.{{sfn|Morgensztern|Boffa|Chen|Dhanasopon|2023|loc="Precursor lesions"}} Their cells grow in three-dimensional clumps, resemble glandular cells, and may produce [[mucin]].{{sfn|Horn|Iams|2022|loc="Pathology"}} About 30% of lung cancers are squamous-cell carcinomas. They typically occur close to large airways.{{sfn|Morgensztern|Boffa|Chen|Dhanasopon|2023|loc="Precursor lesions"}} The tumors consist of sheets of cells, with [[keratinization|layers of keratin]].{{sfn|Horn|Iams|2022|loc="Pathology"}} A hollow cavity and associated [[necrosis|cell death]] are commonly found at the center of the tumor.{{sfn|Morgensztern|Boffa|Chen|Dhanasopon|2023|loc="Precursor lesions"}} Less than 10% of lung cancers are large-cell carcinomas,{{sfn|Horn|Iams|2022|loc="Pathology"}} so named because the cells are large, with excess cytoplasm, large nuclei, and conspicuous [[nucleolus|nucleoli]].{{sfn|Morgensztern|Boffa|Chen|Dhanasopon|2023|loc="Precursor lesions"}} Around 10% of lung cancers are rarer types.{{sfn|Horn|Iams|2022|loc="Pathology"}} These include mixes of the above subtypes like [[adenosquamous carcinoma]], and rare subtypes such as [[lung carcinoid|carcinoid tumors]], and [[Sarcomatoid carcinoma of the lung|sarcomatoid carcinomas]].{{sfn|Morgensztern|Boffa|Chen|Dhanasopon|2023|loc="Precursor lesions"}}

Several lung cancer types are subclassified based on the growth characteristics of the cancer cells. Adenocarcinomas are classified as lepidic (growing along the surface of intact [[alveoli|alveolar]] walls),{{sfn|Jones|2013|loc="Conclusion"}} [[Acinar adenocarcinoma|acinar]] and [[Papillary adenocarcinoma|papillary]], or micropapillary and solid pattern. Lepidic adenocarcinomas tend to be least aggressive, while micropapillary and solid pattern adenocarcinomas are most aggressive.{{sfn|Pastis|Gonzalez|Silvestri|2022|loc="Histology and Prognosis"}}

In addition to examining cell morphology, biopsies are often stained  by [[immunohistochemistry]] to confirm lung cancer classification. SCLCs bear the markers of [[neuroendocrine cell]]s, such as [[chromogranin]], [[synaptophysin]], and [[CD56]].{{sfn|Rudin|Brambilla|Faivre-Finn|Sage|2021|loc="Immunohistochemistry"}} Adenocarcinomas tend to express {{nowrap|[[Napsin-A]]}} and {{nowrap|[[TTF-1]]}}; squamous cell carcinomas lack {{nowrap|Napsin-A}} and {{nowrap|TTF-1}}, but express [[TP63|p63]] and its cancer-specific isoform p40.{{sfn|Horn|Iams|2022|loc="Pathology"}} [[cytokeratin 7|CK7]] and [[cytokeratin 20|CK20]] are also commonly used to differentiate lung cancers. CK20 is found in several cancers, but typically absent from lung cancer. CK7 is present in many lung cancers, but absent from squamous cell carcinomas.{{sfn|Horn|Iams|2022|loc="Immunohistochemistry"}}