Cancer is often described in terms of stages and grades, but it is easy to confuse the two terms. Oncologists use both terms to identify the progression of the disease which helps determine the appropriate treatment.
STAGE
Stage often refers to the size of the tumor as well as whether the tumor has metastatized, or spread. In the U.S., staging is often described according to the TNM classification system devised by Pierre Denoix in the late 1940's and 1950s. This widely accepted system is still used today by the Union for International Cancer Control and the American Committee on Cancer. Not all cancers are staged according to the TNM system. For example, brain cancers, spinal cancers and lymphomas are not staged according to the TNM system.
The TNM system describes tumors in terms of Tumor size (T), Nodal involvement (Nodes), and Metastasis (M).
Tumor Size
Tx: cannot evaluate the primary tumor
Tis: Is stands for 'in situ' a latin word for "in place." This signifies that the cancer cells are localized to the site and have not spread to neighboring tissues.
T0: no evidence of a primary tumor
T1-T4 are used to indicate the size of the tumor and each value varies slightly depending on the type of cancer.
Nodal Involvement
Nx: cannot evaluate lymph nodes
N0: no regional lymph node involvement
N1: regional lymph node involvement
N2-3: further lymph node involvement
Metastasis
M0: no metastasis
M1: metastasis to other organs besides regional lymph nodes
A cancer stage I-IV correlates to a TNM classification.
GRADE
Grade refers to the level of differentiation of the cells and is determined by examining the histology. Cells that are well-differentiated appear similar to normal cells whilst poorly differentiated cells do not present like normal cells. Numerical grades are assigned accordingly. For the most part the higher the grade the less the cells are differentiated.
Further reading
"Tumor Grade." National Cancer Institute. N.p., n.d. Web. 03 Sept. 2015. <http://www.cancer.gov/about-cancer/diagnosis-staging/prognosis/tumor-grade-fact-sheet>.