Diagnosis and Classifications of Lung Cancer
Part one of this series discussed how lung cancer occurs, risk factors, and screening to identify susceptible individuals. If a tumor or nodule is discovered in the lungs, what then?
Typically a person presents with a past history or symptoms that warrant investigation with a chest x-ray. The chest x-ray is read as “abnormal” by the radiologist, who then usually states that a mass cannot be ruled out.
The first step is a computerized tomography (CT) scan of the chest. The purpose of the CT scan is to:
- Confirm that indeed this is a solid mass and not a confluence of airways or pneumonia infiltrate.
- Measure precisely how big the mass is and to identify its characteristics: smooth borders, irregular, speculated, etc. Some of these characteristics will increase the probability of this being a malignant mass.
- Assess if there is extension of this mass into more than just one lobe of the lung or if there is extension outside of the lungs.
- Assess if there are lymph nodes that appear enlarged. This will have implications on spread or metastasis of the cancer.
For all practical purposes all lung cancers are divided into two groups. One group is small cell carcinoma. All the other lung cancer types are referred to collectively as non-small cell lung cancer (NSCLC).
Small cell cancer is classified as “limited” if it’s only present in one lung and “extended” if it’s spread outside of the involved lung. Non-small cell cancer is "staged" by a more complicated system.
The TNM (tumor, node, metastases) staging system was established in 2003 by the International Association for the Study of Lung Cancer. Since then, it’s been revised and updated eight times, and the latest revision will be implemented in January 2018.
The classification system takes into account:
- The size of the mass (T), with T1 being less than 3 cm and T2 greater than 3 cm.
- Lymph node involvement(N). Lymph nodes are connected to lymphatic channels and cancer involvement, when seen in the lymph nodes, implies that cancer cells have the leewayto spread to distant sites in the body (metastasis). This part of the classification system takes into account if the lymph nodes involved are within the lungs (hilar), or located in the chest wall between the lungs (mediastinal), or if the involved lymph nodes are outside the chest in areas like the neck or axillae (armpit).
- Metastases (M) which identifies whether the cancer has been contained within the same lung (M0) or spread to areas outside the lungs (M1)
All this data is coordinated and results in a complicated staging system of I, II, III, IV, and then there’s a further subdivision of some of the stages into a, b, c. The reason for the classification system is to help clinicians determine prognosis and treatment options for each patient’s lung cancer. Usually, staging up to a IIIa classification is considered “amenable to resection by surgery.”
The next step is Positron Emission Tomography (PET scan). A radioactive glucose “tracer” that allows visualization on scan is injected and then a special scan is done to determine the sites of the body that use the glucose in excess of neighboring areas. This excess metabolic activity (measured in SUV units) implies cancer activity and helps to identify if there is spread of the cancer cells.
Next, the patient will undergo pulmonary function testing (PFT). This test evaluates the respiratory status of the patient, to determine if he will be able to withstand the tumor resection. Also of consideration is the fact that some patients with poor respiratory function may not be able to tolerate radiation therapy, since that treatment can cause scarring of the lung (which would further diminish respiratory status in an already compromised patient). The surgeon must also have the ability, at the last moment, to remove the entire lung, if necessary, so assessing respiratory status is crucial. The test will also help to predict respiratory status after surgery (if performed).
These steps are considered preliminary testing. To make the formal diagnosis of lung cancer, a biopsy which directly takes tissue from the mass and a pathology report on the types of cells identified determine if there are atypical cells indicating cancer or not.
This biopsy is done by one of several methods:
A bronchoscope (fiber-optic tube) is inserted through the nose and through the airways of the lungs. When the location of the tumor is reached (determined by a real time x-ray called fluoroscopy), a forceps wire is inserted through the bronchoscope and a piece of tissue (biopsy) is obtained.
Endobronchial ultrasound (EBUS) guided biopsy: If the tumor is very small or outside the bronchial lumen, a real-time ultrasound will help to guide a forceps capture of the biopsy.
When the lesion is at the edge of the lung (where the bronchoscope will not reach), a needle is passed through the outer chest wall to obtain the biopsy, with the help of a CT scan. This is called a Percutaneous Needle Biopsy (PNB).
Video-assisted thorascopic surgery (VATS): In difficult cases, a last resort effort by a thoracic surgeon (requires general anesthesia) introduces a small video camera into the patient’s chest via a scope.
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