Section Editor: Matthew Cecchini MD PhD FRCPC
May 23, 2026
The chest, also called the thorax, contains the lungs and several nearby structures. The lungs bring oxygen into the body and remove carbon dioxide. Each lung is covered by a thin lining called the pleura. The space between the lungs, which holds the heart, the food pipe, and other structures, is called the mediastinum. When tissue is removed from the chest, a pathologist examines it under a microscope and describes what they see in your pathology report.
This page brings together our guides to conditions found in the lungs, pleura, and mediastinum. The articles are grouped by type to help you find the one that matches your diagnosis. Some conditions are cancerous and others are not. Select any article below to learn more.
Cancers of the lung
These diagnoses are cancers that develop in the lung. Many different types can develop here, from the more common cancers to rare ones, and they range widely in how they grow and respond to treatment. The articles explain how each type is diagnosed and what your pathology report describes.
Non-small cell lung cancer is the name for a group of lung cancers that includes adenocarcinoma, squamous cell carcinoma, and others. This article gives an overview of these cancers and what your pathology report describes.
You may find this helpful if your report mentions non-small cell lung cancer or NSCLC, or you want a general overview before reading about a specific type.
Adenocarcinoma is the most common type of lung cancer. It develops from gland-forming cells in the lung. This article explains how it is diagnosed and what the details in your pathology report mean.
You may find this helpful if your report says adenocarcinoma of the lung.
Minimally invasive adenocarcinoma
Minimally invasive adenocarcinoma is a very early form of lung adenocarcinoma with only a small amount of growth into the surrounding tissue. It has an excellent outlook. This article explains what this diagnosis means.
You may find this helpful if your report mentions minimally invasive adenocarcinoma or MIA of the lung.
Mucinous adenocarcinoma is a type of lung adenocarcinoma in which the cancer cells produce mucus. This article explains how it is diagnosed and what your pathology report describes.
You may find this helpful if your report mentions mucinous adenocarcinoma of the lung.
Squamous cell carcinoma is a common type of lung cancer that develops from the flat cells lining the airways. This article explains how it is diagnosed and what the details in your pathology report mean.
You may find this helpful if your report says squamous cell carcinoma of the lung.
Non-keratinizing squamous cell carcinoma
Non-keratinizing squamous cell carcinoma is a type of lung squamous cell carcinoma in which the cells do not produce keratin. This article explains what this diagnosis means and what your report describes.
You may find this helpful if your report mentions non-keratinizing squamous cell carcinoma of the lung.
Adenosquamous carcinoma is a lung cancer that contains two types of cancer cells: adenocarcinoma and squamous cell carcinoma. This article explains what this diagnosis means and what your report describes.
You may find this helpful if your report mentions adenosquamous carcinoma of the lung.
Lymphoepithelial carcinoma is a rare type of lung cancer that contains a large number of immune cells. This article explains how it is diagnosed and what your pathology report describes.
You may find this helpful if your report mentions lymphoepithelial carcinoma of the lung.
NUT carcinoma is a rare, fast-growing cancer defined by a change in a gene called NUTM1. This article explains how it is diagnosed and what your pathology report describes.
You may find this helpful if your report mentions NUT carcinoma or a NUTM1 gene change.
SMARCA4-deficient undifferentiated tumor
SMARCA4-deficient undifferentiated tumor is a rare, fast-growing cancer of the chest defined by the loss of a gene called SMARCA4. This article explains how it is identified and what your report describes.
You may find this helpful if your report mentions a SMARCA4-deficient tumor or loss of BRG1.
A typical carcinoid tumor is a slow-growing neuroendocrine tumor of the lung. It is the lowest-grade type. This article explains how it is diagnosed and what your pathology report describes.
You may find this helpful if your report mentions a typical carcinoid tumor of the lung.
An atypical carcinoid tumor is a neuroendocrine tumor of the lung that grows somewhat faster than a typical carcinoid tumor. This article explains how it is diagnosed and what your report describes.
You may find this helpful if your report mentions an atypical carcinoid tumor of the lung.
Large cell neuroendocrine carcinoma
Large cell neuroendocrine carcinoma is a fast-growing, high-grade neuroendocrine cancer of the lung. This article explains how it is diagnosed and what the details in your pathology report mean.
You may find this helpful if your report mentions large cell neuroendocrine carcinoma, sometimes shortened to LCNEC.
Small cell carcinoma is a fast-growing, high-grade neuroendocrine cancer of the lung. This article explains how it is diagnosed and what the details in your pathology report mean.
You may find this helpful if your report mentions small cell carcinoma or small cell lung cancer (SCLC).
Cancers of the pleura
The pleura is the thin lining that covers the lungs and the inside of the chest wall. These diagnoses describe cancer of the pleura and a related change that can look similar. The articles explain what each diagnosis means.
Mesothelioma is a cancer that develops from the pleura, the thin lining around the lungs. It is often linked to past exposure to asbestos. This article explains how it is diagnosed and what your pathology report describes.
You may find this helpful if your report mentions mesothelioma, or you have a history of asbestos exposure.
Atypical mesothelial proliferation
Atypical mesothelial proliferation is a term used when the cells of the pleura look abnormal, but it is not yet clear whether they are cancer. This article explains what this result means and what happens next.
You may find this helpful if your report mentions an atypical mesothelial proliferation.
Precancerous changes
These diagnoses describe early or precancerous changes in the lung — abnormal cells that have not grown into the surrounding tissue. They have an excellent outlook. The articles explain what each diagnosis means.
Adenocarcinoma in situ is the earliest, non-invasive form of lung adenocarcinoma. The abnormal cells have not yet grown into the surrounding lung tissue. This article explains what this diagnosis means.
You may find this helpful if your report mentions adenocarcinoma in situ or AIS of the lung.
Noncancerous conditions
These diagnoses are not cancer. They include infection, inflammation, injury, and scarring of the lung, as well as other harmless findings. The articles explain what each diagnosis means and what a pathologist looks for.
Pneumonia is an infection that causes inflammation in the air sacs of the lung. This article explains what a pathologist sees in pneumonia and what this diagnosis means.
You may find this helpful if your report mentions pneumonia or signs of infection in the lung.
Acute lung injury describes sudden damage to the lung tissue from causes such as infection, inhaled substances, or illness. This article explains what this diagnosis means.
You may find this helpful if your report mentions acute lung injury.
Diffuse alveolar damage is a pattern of severe, widespread injury to the air sacs of the lung. This article explains what this diagnosis means and what a pathologist looks for.
You may find this helpful if your report mentions diffuse alveolar damage or DAD.
Organizing pneumonia is a pattern of healing in the lung that follows inflammation or injury. Despite its name, it is not always caused by an infection. This article explains what this diagnosis means.
You may find this helpful if your report mentions organizing pneumonia or cryptogenic organizing pneumonia.
Usual interstitial pneumonia is a pattern of scarring (fibrosis) in the lung. It is the pattern seen in a condition called idiopathic pulmonary fibrosis. This article explains what this diagnosis means.
You may find this helpful if your report mentions usual interstitial pneumonia or UIP, or you are being assessed for pulmonary fibrosis.
A carcinoid tumorlet is a tiny cluster of neuroendocrine cells in the lung. It is smaller than a carcinoid tumor and is usually a harmless, incidental finding. This article explains what this diagnosis means.
You may find this helpful if your report mentions a carcinoid tumorlet, often found by chance during testing for another reason.
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