Breast Cancer Grades

Knowing a breast cancer’s grade is important to figure out how fast it’s likely to grow and spread.

What is a breast cancer’s grade?

Cancer cells are given a grade when they are removed from the breast and checked under a microscope. The grade is based on how much the cancer cells look like normal cells.

A lower grade number (1) usually means the cancer is slower-growing and less likely to spread.

A higher number (3) means a faster-growing cancer that’s more likely to spread. The grade is used to help predict your outcome (prognosis) and help figure out what treatments might work best.

Three features are examined and each is assigned a score to determine the histologic grade. The scores are then added. This sum (between 3 and 9) is used to get a grade of 1, 2, or 3, which is noted on your pathology report. Sometimes words such as well differentiated, moderately differentiated, and poorly differentiated are used to describe the grade instead of numbers:

  • Grade 1 or well differentiated (score 3, 4, or 5). The cells are slower-growing, and look more like normal breast tissue.
  • Grade 2 or moderately differentiated (score 6, 7). The cells are growing at a speed of and look like cells somewhere between grades 1 and 3.
  • Grade 3 or poorly differentiated (score 8, 9) . The cancer cells look very different from normal cells and will probably grow and spread faster.

Our information about pathology reports can help you understand details about your breast cancer.   

Grading ductal carcinoma in situ (DCIS)

DCIS is graded only on how abnormal the cancer cells look. Necrosis (areas of dead or dying cancer cells) is also noted. If there is necrosis, it means the tumor is growing quickly.

The term comedocarcinoma is often used to describe DCIS with a lot of necrosis. If a breast duct is filled with a plug of dead and dying cells, the term comedonecrosis may be used. Comedocarcinoma and comedonecrosis are linked to a higher grade of DCIS.

See Understanding Your Pathology Report: Ductal Carcinoma In Situ for more on how DCIS is described.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: September 25, 2017 Last Revised: September 25, 2017

American Cancer Society medical information is copyrighted material. For reprint requests, please see our Content Usage Policy.