How do we know about the prognosis of a given cancer?
The prognosis is the likely outcome of the cancer. Since cancer is a lethal disease, prognosis of patients with cancer is described in terms of expected length of time of survival. A common example is the 5-year survival, defined as the proportion of patients still alive 5 years after the diagnosis of their cancer.
Prognosis of patients firstly depends on the location of the cancer in the body. For example, prostate and breast cancer patients have a better prognosis than patients with lung or pancreas cancer. Secondly the tumor characteristics even within the same location also determine the patient’s prognosis.
To have a better idea of the prognosis of a patient with a given cancer, information on the size of the tumor and the degree of invasion of tumor cells in the body, on the histopathology, and other biological characteristics of the tumor are taken into account. Some characteristics of the patient are also very important.
The stage summarizes the size of the tumor and the degree of invasion of tumor cells in the body. The stage of a cancer is the most important way to evaluate the prognosis. The TNM staging system is used for almost all cancers with a few exceptions like leukemias, lymphomas and brain tumors. The TNM system gives a description of how extensive the cancer is. T describes the size of the tumor and if it has invaded nearby tissue, N describes any lymph nodes that are involved, and M describes metastasis.
The combination of T, N and M will give a stage of 0, I, II, III or IV sometimes with a letter to sub-divide the stages, e.g. stage IIA, stage IIB. For brain tumors, there is no standard staging system. For leukemias, lymphomas and gynecological cancers, specific staging systems exist, but these also give a stage between 0 and IV. In one given type of cancer, the higher the stage, the worse the prognosis. One cannot generalize the stages for every type of cancer, but the following definitions apply for almost all cancers:
- Stage 0 cancers are carcinoma in situ meaning that abnormal cells are present only in the layer of cells in which they initially developed; they do not invade other layers of the organ.
- Stage I cancers are localized to one organ or part of the body.
- Stage II cancers have spread locally.
- Stage III cancers have spread locally and the difference between stage II and stage III depends on the cancer type. More details can be found for each cancer in the cancer tab of the website (click here to view all the different cancers).
Stage IV cancers have metastasized or spread to other organs or throughout the body.
Histopathology is the study of diseased cells and tissues using a microscope. It analyzes the cells taken from a sample of the tumor and determines the speed with which they multiply, how different from normal cells they look, if they have invaded other layers of cells, etc. The prognosis is better when cells do not multiply quickly, when they are not too different from normal cells and when they did not invade other layers of cells.
Biological characteristics of the tumor
Tumor cells in the different cancers have other characteristics that are important for the pprognosis. Some mutated genes in tumor cells have an impact on prognosis and can be identified in a laboratory. Tumor cells also produce proteins in a higher amount than they should. These high amounts of proteins can be found in the cell, on its surface or in the blood. Identifying the mutated genes or the proteins produced by the tumor is important to evaluate the prognosis and to help select the treatment.
A typical example can be found with HER-2 in breast cancer, which is a protein that is over-produced in some breast cancers. These cancers usually have a worse prognosis because they grow and spread quickly. A specific treatment targeting this protein is now available.
Characteristics of patients
In addition, the personal characteristics of the patient will also influence the prognosis. Age, gender, lifestyle, capability of the patient to carry on daily activities - called performance status- presence of other diseases at the same time than the cancer, personal and familial medical history or inherited genetic susceptibility are, amongst others, things that have an impact on survival for almost all cancers. According to the type of cancer, other characteristics will be also important and more details can be found for each cancer in the cancer tab of the website (click here to view all the different cancers).