Michael Johnston
MD, FRCSC, Thoracic Surgeon, Nova Scotia

Lung Cancer Canada Board of Director

Why All These Tests Before Starting Lung Cancer Treatment?

Understanding how lung cancer is treated can be confusing. First of all, lung cancer is not a single disease. It is actually two diseases, called small cell and non-small cell. Non-small cell is more common and makes up over 80% of all lung cancers. Surgery, radiation and chemotherapy are all used in non-small cell lung cancer, with the choice of treatment most dependent on the stage of the disease. Therefore, when lung cancer is diagnosed, or highly suspected, the next order of business is to accurately determine the extent of the disease within the body, i.e. its stage.

The staging system for non-small cell lung cancer is highly refined and widely accepted by oncology specialists around the world. Each stage is described by the size and extent of the tumour within the lung (the T-status), its level of involvement, if any, in lymph nodes within the chest (the N status) and whether the cancer has spread (metastasized) to other areas of the body (the M status). Each descriptor, T, N and M, is given a number that signifies the extent of disease as determined by imaging studies, such as CT scans, bone scan, MRI and occasionally, a PET scan, and by certain biopsy procedures. Putting all of this information together results in a TNM designation that is specific for that individual. For instance, T2N1M0 means that the lung cancer is greater than 3 cm in size, has spread only to lymph nodes within the lung and shows no evidence of spread elsewhere.

Each TNM designation fits within stages 1 through 4, with the higher number signifying more extensive disease. In stage 1, the cancer is confined to the original site within the lung and there is no sign of spread to lymph nodes (N0) or elsewhere (M0). Stage 2 has spread to lymph nodes within the lung (N1), such as in the example cited above. In stage 3 the cancer has spread to lymph nodes in the middle of the chest (the mediastinum) (N2 or N3), but not elsewhere (M0). And in stage 4 the cancer has spread to other areas in the body (M1).

In general stages 1 and 2 are treated by surgery, stage 3 by a combination of radiation, chemotherapy and possibly surgery and stage 4 by chemotherapy and radiation. Unfortunately, the staging system is only as accurate as the tests that are used to determine the stage and no test is yet able to detect minute spread of cancer cells.