Adenocarcinoma in situ of the lung

by Jason Wasserman MD PhD FRCPC
February 9, 2023


Adenocarcinoma in situ (AIS) is a type of non-invasive lung cancer. It is called non-invasive because the tumour cells have not spread beyond the surface of the small airspaces called alveoli in the lung. For a tumour to be called adenocarcinoma in situ, it cannot be larger than 3.0 cm in size. If left untreated, this condition can turn into invasive adenocarcinoma over time.

lung histology

What causes adenocarcinoma in situ?

The leading cause of adenocarcinoma in situ in the lung is tobacco smoking. Other less common causes include radon exposure, occupational agents, and outdoor air pollution.

What are the symptoms of adenocarcinoma in situ of the lung?

Because these tumours are small and non-invasive, adenocarcinoma in situ on its own is not associated with any specific symptoms.

Is adenocarcinoma in situ of the lung a type of cancer?

Adenocarcinoma in situ is a non-invasive type of lung cancer. That means that the cells in the tumour look very similar to the cells in invasive adenocarcinoma of the lung. However, in contrast to invasive adenocarcinoma, the cells in adenocarcinoma in situ are unable to spread to other parts of the body such as lymph nodes.

How is this diagnosis made?

The diagnosis of adenocarcinoma in situ of the lung can only be made after the entire tumour has been surgically removed and sent to a pathologist for examination under the microscope. The diagnosis cannot be made after a small sample of the tumour is removed in a biopsy or when cytology is performed. Your pathologist will carefully examine the tumour to make sure there are no areas of invasion before making the diagnosis of AIS.

Microscopic features of adenocarcinoma in situ of the lung

The inside of the lung is made up of many small airspaces called alveoli. When examined under the microscope, the tumour cells in adenocarcinoma in situ are seen covering the inside surface of the alveoli. Pathologists use the term lepidic to describe this pattern of growth. The tumour cells are typically larger and darker than the specialized pneumocytes that normally line the alveoli. Unlike minimally invasive adenocarcinoma, there is no evidence of invasion into surrounding tissues.

adenocarcinoma in situ lung
Adenocarcinoma in situ in the lung.

About this article

This article was written by doctors to help you read and understand your pathology report. Contact us if you have any questions about this article or your pathology report. Read this article for a more general introduction to the parts of a typical pathology report.

Other helpful resources

Atlas of Pathology
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