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Pathology report

Understanding your pathology report

The pathology report provides detailed information about your breast biopsy or the tissue removed at your breast cancer surgery.

Most cancers begin in the breast’s mild ducts (ductal carcinoma or ductal cancer) or milk-producing glands (lobular carcinoma or lobular cancer).

The pathology report

Normal Breast Duct and Lobule 

The breast duct is like a plumbing pipe in the breast — milk flows through its hollow center. It is surrounded by normal breast duct cells. The lobules are at the end of the ducts and make the milk during breast feeding (lactation).


The normal cells can sometimes grow inside the duct and this is called hyperplasia. If the cells look atypical then it is called Atypical Ductal Hyperplasia which is not cancer, but is a risk factor for developing cancer.

Ductal Carcinoma In Situ (DCIS)

The cells are cancerous, but are confined inside the duct (in situ) and have not spread out of the duct. You typically cannot feel this, and it usually shows up on a mammogram as “microcalcifications.”

DCIS and Microinvasion 

Eventually the cancer cells will pass out of the duct, but if caught at this stage, there are only a small number of cancer cells present. You typically cannot feel this either, and it usually shows up on a mammogram.

Invasive Ductal Cancer (or Carcinoma) 

The cancer cells continue to grow into the tissue surrounding a duct or lobule, eventually creating a lump that can be felt in the breast. It can take years before the lump is big enough to feel. Mammograms will often find the lumps before they can be felt.

Tumor Grade

Tumor grade is a classification system that the pathologists use to describe how abnormal the cancer cells look under a microscope and how quickly the tumor is likely to grow and spread. Grade is also called differentiation and describes how much the breast cancer cells resemble the normal breast cells.

Tumor grade should not be confused with the stage of a cancer. Cancer stage refers to the extent of the cancer based on the tumor size, the lymph node involvement; and whether the cancer has spread to other parts of the body. It typically cannot be determined until after surgery when the actual size and lymph node involvement is determined.

Tumor grade is based on the microscopic appearance of cancer cells. Pathologists commonly describe breast tumor grade by three degrees of severity: Grades 1, 2 and 3 or they may be described as well-differentiated (Grade 1); moderately-differentiated (Grade 2) or poorly differentiated (Grade 3). The cells of Grade 1 tumors resemble normal cells and tend to grow and multiply slowly. Grade 1 tumors are generally considered the least aggressive in behavior. Conversely, the cells of Grade 3 tumors look very different than normal cells of the same type. Grade 3 tumors tend to grow rapidly and spread faster than tumors with a lower grade.

Tumor Markers

The pathologist and lab will also check your tumor cells to see if they are sensitive to estrogen or progesterone. If your tumor is sensitive then you may be given medications that block hormones from getting to your cancer or medications that stop estrogen from being made.

Your tumor is also checked for HER2 which is a protein that controls cell growth and repair. Cancer cells that have high levels of HER2 tend to grow rapidly and respond well to anti-HER2 therapy (herceptin). About 20 percent of invasive breast cancers will have this marker.


The pathologist will check the area surrounding the edge of the tumor to make sure the cancer was completely removed.

Negative Margin: Cancer was entirely removed during surgery

Positive Margin: Residual cancer cells remain following surgery and typically more surgery is required

Close Margin: The cancer cells are too close to the margin to ensure all of the cancer was removed