The following is a list of specific tumor characteristics determined by microscopic analysis of tissue taken from the breast cancer. It is the
pathologist who is responsible for performing the microscopic examination.

Tumor Size

The size of a breast cancer is one of the most important determinants of the outcome for a breast cancer patient. The smaller the tumor, the better the prognosis, or expected outcome for the patient. Tumor size is measured in centimeters (2.54 centimeters = 1 inch and 10 millimeters = 1 centimeter) and can only be accurately measured when the tumor is completely removed at surgery and examined by the pathologist.

Tumor Grade

The pathologist examining the tumor under the microscope describes the appearance of the malignant cells. Nuclear grade is described as 1, 2 or 3 and histologic grade is referred to as I, II or III. The more aggressive ("less friendly") appearing cells are grade 3 (III) and the least aggressive ("friendlier") appearing cells are grade 1(I). Grade 2 (II) cells are characterized as intermediate ("in the middle").

Lymphovascular Invasion

Breast cancers have a blood supply like normal tissue and organs. Tumors also have lymphatic channels running through them, which serve as a circulatory system in the body for tissue fluid and proteins separate from the blood circulation. If cancer cells under the microscope appear to invade into the blood vessels or lymphatic channels of the tumor, the possibility that cancer cells have spread to the lymph nodes or other areas in the body increases. This is called lymphovascular invasion or LVI.

Proliferative Index

Breast tumors are analyzed to determine what percentage of cells are dividing (making new tumor cells). A proliferative index is reported to describe the number of cells that are actively growing. A low proliferative index means a slower growth rate and is considered more favorable than a high proliferative index as follows:

	0-12%		low/favorable
	13-35%		intermediate/borderline
	>36%		high/unfavorable

Not surprisingly a low proliferative index tends to occur in tumors with low tumor grade and positive ER and PR.

Margins

Treatment of breast cancer includes complete removal of the tumor in the breast. At the time of surgical removal, the surgeon will remove a rim of normal appearing tissue surrounding the cancer. The pathologist will look at the tissue under the microscope to determine if the normal looking tissue has any cancer cells surrounding them present. The distance between tumor cells and the edge of the normal tissue is measured. This is called the tumor margin. A close margin has a higher chance of recurrence, and a margin cutting across tumor (positive margin) has a very high chance of recurrence of cancer in the breast. Usually additional surgery is recommended if margins are positive or very close in multiple areas of a breast excision.