Neoplasms are human cells that reproduce uncontrollably crowd out normal ones, and compete for space and, in some cases, nutrients. Some are benign and non-cancerous, while others are malignant, metastatic cells capable of rapid growth, moving into adjacent tissues and organs or other areas. A cancerous neoplasm consists of a mass or tumor of abnormal cells, commonly classified as primary or secondary. Primary neoplasms are those occurring at the site where growth first began, as neoplasms of a secondary nature proliferate and move to other places. The type of cancer is based on where it originates, regardless of where it spreads; for example, lung cancer which spreads into the lymph nodes is diagnosed as "metastatic lung cancer."
With the objective of determining course of treatment and a patient's probable outcomes, physicians typically assign a stage to the cancer diagnosis. Staging is a way of coming to a conclusion about how far along or advanced the condition is, bringing into consideration of whether or not the tumor is a primary neoplasm and where it is located. Also of importance to this process includes finding out if lymph nodes have been affected, as well as mass sizes and how many there are, if more than one has been found.
Tumor grading, not to be confused with staging, has to do with the degree to which cells appear to be abnormal as determined by a pathologist, a medical doctor who specializes in treating conditions of diseased tissue, particularly expert in diagnosing illness through microscopic and imaging studies. Once the tumor is biopsied, it can be studied under the microscope and, based upon what the pathologist observes, a conclusion about grading of the primary neoplasm can be determined. Grades are given as one of five possibilities — GX, G1, G2, G3, or G4 — progressing in degree of abnormality and growth rate, with G4 consisting of cells exhibiting fast growth and being the most abnormal. Certain types of cancer require the use of a different kind of grading system, such as prostate and breast cancer. Grading of a primary neoplasm is included in the staging process.
Spreading of malignant cells, called metastasis, is accomplished primarily when cells break away from the original site typically through movement into the blood and lymph. Tumor cells classified as secondary tend to have the same appearance and structure as those of the primary neoplasm, although are much more difficult to treat. Of the millions who die from cancer worldwide yearly as of 2011, most die from secondary, metastatic cancer.