Adenocarcinoma in situ of the lung

by Jason Wasserman MD PhD FRCPC
February 9, 2023

What is adenocarcinoma in situ of the lung?

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. In order for a tumour to be called AIS, it cannot be larger than 3.0 cm in size. If left untreated, this condition can turn into invasive adenocarcinoma over time.

What causes adenocarcinoma in situ?

The leading cause of AIS 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, AIS on its own is not associated with any specific symptoms.

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

AIS 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 AIS are unable to spread to other parts of the body such as lymph nodes.

How do pathologists make the diagnosis of adenocarcinoma in situ?

The diagnosis of AIS 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.

What does adenocarcinoma in situ look like under the microscope?

The inside of the lung is made up of many small airspaces called alveoli. When examined under the microscope, the tumour cells in AIS 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.