Cancer can be diagnosed at any stage. It may appear as a local disease or systemic compromise of multiple organs (metastatic disease). Staging is the method used to evaluate cancer-spreading behavior. It might progress from local tumor to regional lymph nodes and metastatic disease. The staging is based on international criteria used to better describe the patient prognosis. It also guides the treatment's recommendation. When browsing the following icons, you will better understand the importance of the staging in guiding cancer treatment decisions.
Cancer is usually diagnosed in the primary tumor. However, spreading of cancer cells is the main characteristic of malignant tumors, which occurs predominantly through blood or lymphatic routes. Cancer could be diagnosed at anytime during its natural history. The evaluation of the disease extent is called staging. The stage is based on the primary tumor location and size, which is described by the letter T. The stage also includes lymphatic spreading, designated by the letter N and blood metastatic disease, which is represented by the letter M. The combination of the three descriptors creates a classification called TNM. Based on TNM, each cancer type is further categorized from stage I up to stage IV, indicating progressive disease involvement. For each stage there is a specific treatment recommendation and a higher or lower cure rate.
Based on the pathological diagnosis and tumor natural history, the attending physician decides which exams are necessary to evaluate the extent of the disease. The tests used for cancer staging include image methods such as X-ray, computed tomography (CT) and magnetic resonance imaging (MRI). More recently, PET-CT has been included, which evaluates both tumor anatomy and metabolic function. Eventually, even more invasive methods such as bone marrow biopsy are required, especially in leukemia and lymphomas. Staging abdominal surgery is routinely used in ovarian cancer. Physicians are very concern about precise cancer staging, selecting the most accurate exams for each specific tumor biological behavior.
Staging follows international classification systems, which describe progressive tumor local invasion and systemic spread. The most used are the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC). Staging consists on universal communication criteria with precise implication on cancer prognosis and treatment. Both AJCC and UICC are based on TNM criteria. The descriptor T shows the tumor size and invasion of surrounding tissues or organs. The descriptor N is associated with detection of cancer cells in lymphatic nodes. The descriptor M characterizes the spread through the bloodstream, affecting organs located away from the primary tumor, which is called metastases. For each tumor there are specific criteria that can be found in the international system AJCC, which might be accessed through www.cancerstaging.org. The correct treatment recommendation and its curative or palliative intention are based on the cancer stage.
Cancer cells can be in different stages of differentiation. Undifferentiated cells tend to be more aggressive, expressing a high proliferative index. Differentiated cells resemble to the original shape. During tumorigenesis, normal cells are transformed in cancer cells. Under the microscopy the chance to point out the original tissue varies according the cell differentiation grade. The tumor should be classified according its histological grade. Lower grades are associated with better prognosis. The best example is the Gleason tumor classification used in prostate cancer. A tumor Gleason 4 is less aggressive than a tumor Gleason 8. In some tumors, the histologic grade has been already incorporated in the TNM classification, adding the descriptor G. You can better understand the prognosis importance of the descriptor G assessing the staging for soft tissue sarcomas in AJCC.
Some solid tumors produce circulating markers, which might give an idea of the extent of the disease. These markers are measured in blood tests. They have little diagnostic value, but have defined implications for prognosis and treatment. An example is the carcinoembryonic antigen (CEA). The CEA is a circulating tumor marker, very useful in the follow-up of colorectal cancer. When it remains high after tumor's surgical removal, might indicate persistent disease. The CA-125 is widely used for monitoring treatment of ovarian cancer. The CA-125 should normalize after a well-succeeded ovarian cancer treatment. Beta-HCG and alpha-fetoprotein markers are used for monitoring patients with testicular tumors and cure is obtained only after normalizing these markers. The LDH is very important in monitoring lymphomas. The PSA is used in prostate cancer. However, caution is required in its interpretation. A high PSA does not diagnose prostate cancer. PSA is not specific to cancer and might be abnormally elevated in benign prostatic hyperplasia, which consists in a large prostate, but without malignant tumor. However, when cancer is already diagnosed, a rising PSA is directly related to the tumor extension. After surgical treatment of prostate cancer, the PSA should go down to zero, indicating that the surgery was radical, which means that the entire prostate tissue was removed. Although tumor markers do not participate directly in the AJCC, often very high values indicate more advanced disease.