• Anatomical Overview
• Types of Cancer
• What is Cancer?

Each organ in the body-stomach, liver, kidney, bladder, even skin-is made up of millions of cells. Cells are constantly dividing to replace the old or damaged ones, so that there is a constant "cell turnover" taking place. Cell turnover is very important to keep organs functioning properly.

In ways scientists do not completely understand, these cells will divide, making more cells, only when it is necessary. Somehow, the cells know when to stop dividing. If a cell within a given organ continues to divide erroneously, an abnormal growth-or tumor-will develop. However, a tumor alone is NOT cancer. In order to be designated as "cancer", the potential for invasion must be present.

Just as there is a physical boundary between organs in the body, there are also boundaries within the organ itself. As discussed above, the bladder wall has several tissue layers- the transitional epithelium, the muscular layer, and the fat layer-each separated from one another by fibrous bands known as connective tissue. Once the abnormally replicating cells making up a tumor penetrate into a different layer-say epithelial cells growing into the muscle layer- invasion has taken place. In addition, these cells can invade into blood vessels, which can carry them to distant organs where they can grow into new tumors, or metastases. In bladder cancer, the most common cell type to become a cancer is the transitional epithelial cell, designated as transitional cell carcinoma or TCC.

When defining an invasive cancer, it is important to understand the tumor grade. Grade is a microscopic designation-in this case low or high grade-an attempt to classify how much the appearance and arrangement of cells differ from their once normal state. Abnormally behaving cells may or may not appear like their normal predecessors, from which they are derived. For example, cells that compose a low grade TCC may appear very similarly to surrounding normal transitional epithelium, except that the cancer transitional cells invade. Indeed, their behavior belies their rather normal appearance. On the other hand, a high grade TCC will microscopically appear vastly different from its once normal appearing state. Indeed, a high grade tumor has lost any resemblance to its normal tissue type. High grade cancers are more likely to be rapidly invasive and therefore poses a greater threat of disease progression and death in the absence of effective treatment.