Cancer is not one disease, but a group of diseases defined by abnormal growth of the cells. Cancer type refers to the organ or type of cell where cancer started. In some cancers such as leukemia the cells do not form tumors, instead they form in the blood or bone marrow.
Various staging systems are used to determine what stage a cancer diagnoses may be in. The most common is the T N M format:
T refers to the size of the tumor
N indicates the number of lymph nodes involved at the time
M refers to the presence of the metasis.
STAGE 0 = precancer
STAGE 1= small cancer located in organ
STAGE 2= larger cancer that may have spread to lymph nodes
STAGE 3 = cancer in the lymph nodes
STAGE 4 = cancer present in a different organ from where it originated.