This article was last reviewed and updated on September 13, 2019
by Jason Wasserman, MD PhD FRCPC
The normal lungs and airways
The lungs are large organs found in our chest. They are connected to the outside of the body by hollow tubes called airways. Air travels from our mouth and nose down the airways into the lungs.
The lungs are a paired organ which means there is one on each side of the body (right and left). Each lung is divided into lobes. The right lung has three lobes, upper, middle, and lower. The left lung has only two lobes, upper and lower.
The body needs oxygen to produce energy. In the lungs, oxygen leaves the air and enters our blood. The oxygen is then delivered to the whole body by the blood. The production of energy creates carbon dioxide which is removed from the blood in the lungs.
The inner surface of the smaller airways are lined by rectangular shaped shaped that have small projections on their surface called cilia. These cells form a barrier that pathologists call respiratory type epithelium. Over time, the cells in the respiratory type epithelium can change into squamous cells. This process is called metaplasia.
The lungs are made up of thousands of small air filled spaces. These air filled spaces are lined by a single layer of small flat cells called pneumocytes. The tissue just below the pneumocytes is called stroma.
What is squamous cell carcinoma?
Squamous cell carcinoma is a type of lung cancer. Squamous cell carcinoma starts from the squamous cell that line the inside of the large or small airways.
These tumours develop when the squamous cells become damaged (often by the chemicals in cigarette smoke) and start to grow abnormally. All tumours start within the epithelium on the inside of an airway but most quickly grow into the surrounding tissue. The movement of cancer cells from airways into the surrounding lung tissue is called invasion.
The diagnosis of squamous cell carcinoma is usually made after a small sample of tissue is removed in a procedure called a biopsy or a fine needle aspiration (FNA). Surgery may then be performed to remove the entire tumour.
You may see the name of the procedure in your pathology report. The name will depend on the amount of tissue removed.
Procedure names include:
Your pathologist may perform a test called immunohistochemistry to confirm the diagnosis. The results will be described as positive (reactive) or negative (non-reactive).
Squamous cell carcinoma usually shows the following results:
Why is this important? This test is used to confirm the diagnosis of squamous cell carcinoma. Your report may not include all of the results shown above.
This is the size of the tumour measured in centimeters (cm). The size of the tumour can only be measured after the entire tumour has been removed. The tumour is measured in three dimensions but only the largest dimension may be described in your pathology report.
Why is this important? The tumour size is used to determine the tumour stage (see Pathologic stage below).
In some situations, more than one tumour is found when the lung tissue is examined under the microscope. When this happens, each tumour will be described separately in your report.
There are two possible explanations for finding more than one tumour:
Why is this important? Tumour nodules increase the tumour stage while metastatic disease increases the metastatic stage (see Pathologic stage below). Both are associated with worse prognosis.
The lungs are surrounded by a thin tissue called pleura. The pleura has both an inner and outer lining. The inner lining touches the lung and the outer lining faces an open cavity called the pleural space.
Tumours that break through the inner lining of the pleura can spread into the pleural space and from there to other parts of the body.
Your pathologist will closely examine all the sections of pleura under the microscope to see if any cancer cells have passed the inner lining of the pleural. The movement of cancer cells through the inner lining of the pleural is called pleural invasion.
Why is this important? Pleural invasion increase the tumour stage (see Pathologic stage below) and is associated with worse prognosis.
Invasion of organs outside of the lung
The lung is surrounded by several organs including bones, muscles, diaphragm, heart, esophagus, and trachea. Large tumours can grow grow beyond the lung and into any of these surrounding organs.
Why is this important? Invasion into another organ increases the tumour stage (see Pathologic stage below) and is associated with worse prognosis.
Treatment effect is described in your report only if you received either chemotherapy or radiation therapy prior to surgery to remove the tumour. In order to determine the treatment effect, your pathologist will measure the amount of living (viable) tumour and express that number as a percentage of the original tumour.
For example if your pathologist finds 1 cm of viable tumour and the original tumour was 10 cm, the percentage of viable tumour is 10%.
Blood moves around the body through long thin tubes called blood vessels. Another type of fluid called lymph which contains waste and immune cells moves around the body through lymphatic channels.
Cancer cells can use blood vessels and lymphatics to travel away from the tumour to other parts of the body. The movement of cancer cells from the tumour to another part of the body is called metastasis.
Before cancer cells can metastasize, they need to enter a blood vessel or lymphatic. This is called lymphovascular invasion.
Why is this important? Lymphovascular invasion increases the risk that cancer cells will be found in a lymph node or a distant part of the body such as the lungs.
In order to remove a tumour from the lung, normal lung tissue, blood vessels, and airways all have to be cut. Any tissue that is cut when removing a tumour is called a margin and all margins are examined closely for any microscopic evidence of tumour.
For squamous cell carcinoma, a margin is considered positive when there are cancer cells at the edge of the cut tissue. If no cancer cells are seen at any of the cut edges of tissue, the margins are called negative.
Margins will only be described in your report after the entire tumour has been removed.
Why is this important? A positive margin is associated with a higher risk that the cancer will re-grow (local recurrence) in the same site after treatment.
Lymph nodes are small immune organs located throughout the body. Cancer cells can travel from the tumour to a lymph node through lymphatic channels located in and around the tumour (see Lymphovascular invasion above). The movement of cancer cells from the tumour to a lymph node is called a metastasis.
Lymph nodes from the neck, chest, and lungs may be removed at the same time as the tumour. These lymph nodes are divided into areas called stations. There are 14 different stations in the neck, chest, and lungs. Your pathology report will describe the number of lymph nodes examined from each station.
Stations that may be described in your report:
Your pathologist will carefully examine each lymph node for cancer cells. Lymph nodes that contain cancer cells are often called positive while those that do not contain any cancer cells are called negative. If cancer cells are found in a lymph node, the station of the positive lymph node will be described in your report.
Why is this important? Finding cancer cells in a lymph node increases the nodal stage (see Pathologic stage below) and is associated with worse prognosis. The nodal stage selected will depend on where the lymph node with cancer cells was located (the station).
The pathologic stage for squamous cell carcinoma is based on the TNM staging system, an internationally recognized system originally created by the American Joint Committee on Cancer.
This system uses information about the primary tumour (T), lymph nodes (N), and distant metastatic disease (M) to determine the complete pathologic stage (pTNM). Your pathologist will examine the tissue submitted and give each part a number. In general, a higher number means more advanced disease and worse prognosis.
The pathologic stage will only be described in your report after the entire tumour has been removed. It will not be included after a biopsy.
Tumour stage (pT) for squamous cell carcinoma
Squamous cell carcinoma is given a tumour stage between 1 and 4 based on the size of the tumour, the number of tumours found in the tissue examined, and whether the tumour has broken through the pleural or has spread to organs around the lungs.
Nodal stage (pN) for squamous cell carcinoma
Squamous cell carcinoma is given a nodal stage between 0 and 3 based on the presence or absence of cancer cells in a lymph node and the location of the lymph nodes that contain cancer cells.
Metastatic stage (pM) for squamous cell carcinoma
Squamous cell carcinoma is given a metastatic stage of 0 or 1 based on the presence of cancer cells in the lung on the opposite side of the body or at a distant body site (for example the brain).
The metastatic stage can only be determined if tissue from the opposite lung or distant site is sent for pathological examination. Because this tissue is rarely present, the metastatic stage cannot be determined and is listed as pMX.