Staging and grading

Tumor biopsies (tissue samples) are examined microscopically to determine the type and degree of development. A grading scale is used, usually Grade I to Grade IV, to describe tissue differentiation. Tumors that are well differentiated (it still looks like the original source tissue) generally have a good clinical outcome. Tumors that are poorly differentiated (the tissue has taken on a more primitive structure and may not resemble its original tissue) generally have a poorer outcome. The clinical stage of a tumor is determined by physical exam (Can you feel the tumor? Can you palpate (feel) lymph nodes? Is the tumor fixed in place (adherent to other structures)? Imaging (CT, MRI) is also an essential tool. The stage of the tumor determines if the tumor has invaded surrounding tissue, involved lymphatics (drainage channels for cell fluids other than blood) and whether the cancer has metastasized to other sites in the body.

A staging system using the letters T, N, M is also used in conjunction with Grading. “T” indicates size of tumor; “N” whether the cancer has spread into lymph nodes; “M” whether cancer cells have metastasized to other organs and areas. For example, a melanoma T2N0M0 describes a skin cancer that is between 1.0 and 2.0 mm in thickness, but has not spread into lymph nodes or other areas of the body.

Grading and staging tumors are important ways to predict the “prognosis” (progress and outcome of the disease), and which types of treatments may most likely succeed. In general, low grade tumors that have not invaded tissues, have not involved lymph nodes (negative nodes) and have not metastasized would be expected to have a better prognosis than a high grade tumor that has invaded tissues, has invaded lymphatics (positive nodes) and has metastasized. However, the prognosis of any individual patient is much more complicated than described here. Complicating factors include the general health of the patient, the effectiveness of their immune system and available treatment options. Some tumor types are very “aggressive” and are highly resistant to treatment.