Understanding Your Breast Cancer Pathology Report

Medically reviewed by Steffini Stalos, DO

A pathologist (a doctor who studies body tissues) diagnoses breast cancer by identifying cancer cells in breast tissue. The tissue may be obtained from surgery or a biopsy (a sample of the abnormal breast tissue).

Once breast cancer is diagnosed, the pathologist performs additional tests on the breast tissue. These tests aim to understand the cancer better, including its type, how fast it's expected to grow, and what treatments it may respond to.

Navigating a breast cancer diagnosis and the wealth of information that comes with it is often overwhelming. This article will hopefully help you better understand and "decode" the medical language you might read in a breast cancer pathology report.

Specimen

A pathologist provides details about the breast tissue sample, often called a specimen.

Such information might include:

• The date the tissue sample/specimen was removed.

• The breast location where the sample/specimen was removed (e.g., right or left breast)

• The type of biopsy or surgery (e.g., mastectomy or lumpectomy) performed.
  

Related: What Are the Types of Breast Biopsies?

Clinical History

This section of the pathology report summarizes how the cancer was discovered, such as through a screening mammogram. Relevant medical history, like a personal or family history of breast cancer, is also disclosed.

Related: What Are the Early Signs of Breast Cancer?

Gross Description

A gross description is what the pathologist sees with their naked eyes before looking at the tissue under a microscope. In this section, a pathologist reports the tissue's size in millimeters (mm), weight, color, texture, and consistency. This can include the presence of friability (is able to be broken up) or exudate (seepage). They also report how many lymph nodes were received.

Related: The Parts of the Breast

Noninvasive vs. Invasive

This part of the report states whether the cancer is noninvasive or invasive.

Noninvasive breast cancer is also called in situ breast cancer, meaning the cancer has stayed in the same place where it began growing.

Ductal carcinoma in situ (DCIS) is a noninvasive breast cancer that starts and remains in a milk duct. It's the earliest form of breast cancer, making up around 20% of new breast cancer diagnoses.

Lobular carcinoma in situ (LCIS) is a noncancerous (benign) breast condition associated with cells that resemble cancerous cells within the lining of the lobules (milk-producing glands). Compared to the general population, LCIS increases a person's future risk of developing invasive breast cancer by approximately 9 to 10 times.

Invasive breast cancer makes up around 75% of all breast cancers and occurs when the cancer cells have spread to surrounding breast tissue. There are several invasive breast cancers, the most common being invasive ductal carcinoma.

Tumor Stage

Tumor stage refers to the spread or extent of cancer in a person's body.

Breast cancer stages range from stage 0 (carcinoma in situ) to stage 4 (metastatic). Metastatic breast cancer is when the cancer has spread to distant parts of the body, most commonly the bones, brain, lungs, or liver.

Overall, the lower the stage number, the less the cancer has spread.

The tumor, node, metastasis (TNM) system is an internationally accepted method for determining breast cancer stage.

"T" stands for the tumor size and is defined as follows:

• Tis: Carcinoma in situ

• T1: Tumor is less than 2 centimeters (cm) across.

• T2: Tumor is more than 2 cm but less than 5 cm across.

• T3: Tumor is greater than 5 cm.

• T4: Tumor of any size grown into the skin or chest wall.

"N" indicates whether the cancer has spread to nearby lymph nodes, which are tiny bean-shaped structures that filter lymph (clear fluid that drains from tissues).

Lymph Node Status

The lymph nodes under your arm (axillary lymph nodes) are where breast cancer usually goes first if it spreads. These lymph nodes may be sampled or removed simultaneously with your breast biopsy or surgery and checked for cancer cells.

The pathologist reports "N" as N0, N1, N2, or N3. The higher the number after N, the more lymph node involvement.

"M" represents metastasis, meaning whether the cancer has spread beyond the breast and nearby lymph nodes to other parts of the body like the bones or brain. Various blood and imaging tests help determine metastasis.

Related: Breast Cancer Staging: What You Need To Know

Tumor Grade

Tumor grade describes the degree to which the cancer cells look like normal, healthy cells. Overall, the lower the grade, the less aggressive the breast cancer is; the higher the grade, the more aggressive. An aggressive cancer is likely to grow and spread rapidly.

Related: Cancer Cells vs. Normal Cells: How Are They Different?

Ductal Carcinoma In Situ (DCIS) Grade

DCIS grade is scored as 1, 2, or 3. The terms "low-grade," "intermediate-grade," or "high-grade" are also sometimes used on the pathology report.

• Grade 1, or low-grade: The cancer cells resemble healthy breast cells and are slow-growing

• Grade 2, or intermediate-grade: The cancer cells resemble breast cells between grades 1 and 3 in appearance and growth.

• Grade 3, or high-grade: The cancer cells do not look like healthy breast cells and are growing fast.

Lobular Carcinoma In Situ (LCIS) Grade

Unlike DCIS, LCIS rarely develops into invasive breast cancer if left untreated. Having LCIS is generally considered a risk factor, not a precancer diagnosis.

The pathologist will examine the LCIS cells and report on a pathology report if they appear pleomorphic or necrotic, as these features can affect the treatment plan.

The variant pleomorphic LCIS differs from classic LCIS because the cells are larger and more abnormal. LCIS with necrosis (also known as florid LCIS) is another variant in which the cells grow together, forming a mass with an area of dead cells in the middle.

Invasive Breast Cancer Grade

The grading system for invasive breast cancer involves the pathologist looking for three features within the tumor under the microscope.

The three features are first scored individually like so:

• Gland formation (1, 2, or 3): The amount of glandular/tubular structures present in normal breast tissue. The lower the score, the more the cancer area resembles normal breast tissue.

• Nuclear grade: How closely the cells' nuclei, which contains cell DNA, resemble that of normal breast cells in size and shape. The lower the score, the more closely they resemble normal breast cells.

• Mitotic count: The number of dividing cancer cells in the most active part of the tumor. The lower the score, the less number of dividing cells there are.

Then, the pathologist adds the individual scores to get a number (called the Nottingham score) between 3 and 9, as follows:

• Grade 1, or well-differentiated: Represents a score of 3 to 5, meaning the cancer cells resemble healthy breast cells and are slow-growing

• Grade 2, or moderately differentiated: Represents a score of 6 or 7, meaning the cancer cells resemble breast cells between grades 1 and 3 in appearance and growth.

• Grade 3, or poorly differentiated: Represents a score of 8 or 9, meaning the cancer cells do not look like healthy breast cells and are growing fast.
  

Learn More: Tumor Grades and Breast Cancer

Hormone Receptor Status

Hormone receptors are proteins on the surface of breast cancer cells. Estrogen or progesterone can bind to the receptors, stimulating cell growth.

Knowing whether a breast tumor has hormone receptors helps determine the cancer stage and whether the tumor can be treated with endocrine (hormone) therapy.

Breast tumors with estrogen receptors (ER+) or progesterone receptors (PR+) are hormone receptor-positive (HR+). Tumors with very few or no estrogen or progesterone receptors are hormone receptor-negative (HR-).

How Common Is Hormone Receptor-Positive Breast Cancer?

Approximately 80% of female breast cancer cases are hormone receptor-positive. (Note that the terms for sex or gender from the cited source are used.)

The presence of hormone receptors on breast tumors is measured by immunohistochemistry (IHC), a laboratory test where a pathologist uses antibodies (marking molecules) to identify various proteins on cell surfaces.

Different pathology laboratories can have slightly distinct ways of reporting the hormone receptor status of the breast tumor. For example, hormone receptor status might be reported as a number or percentage between 0 and 100 or a number (0, 1+, 2+, 3+).

Regardless of the unique scoring, the cancer is definitively HR- when the score is 0. Moreover, the higher the number, the more hormone receptors are present on the breast cancer cells.

Learn More: Hormone Receptor Status in Breast Cancer

HER2 Status

Invasive or metastatic (has spread to distant parts of the body) breast tumors are also tested for human epidermal growth factor receptor 2 (HER2). HER2 is a protein that regulates cell growth and is found on normal cells' surfaces.

Breast cancers that overproduce the HER2 protein are HER2-positive, whereas breast cancers that make minimal or no HER2 protein are HER2-negative.

There is also a subtype called HER2-low that has some HER2 protein on the surface of the cancer cells but not enough to be considered HER2-positive.

Like hormone receptor status, the presence and level of HER2 protein help determine the cancer stage and whether the cancer can be treated with specific drugs, namely HER2-targeted therapies.

HER2 status is determined by performing immunohistochemistry (IHC) and subjectively scoring the amount of HER2 protein present on the cancer cells.

• If the score is 0 or 1+, the cancer is HER2-negative.
  

• If the score is 3+, the cancer is HER2-positive.

If the score is 2+, the result is considered equivocal, and a second test, fluorescence in situ hybridization (FISH), is performed.

FISH detects the number of HER2 gene copies in the cancer cells. If FISH is positive (two copies of the gene are present), the cancer is HER2-positive; if negative, the tumor is HER2-low.

Related: HER2-Low Breast Cancer Treatment

Tumor Margins

Tumor margins are only reported if the breast tumor is surgically removed, not biopsied. The pathologist checks tumor margins by examining the outer edges of the specimen under a microscope to see if cancer cells are present. Margins may be either of the following:

• Positive margins indicate cancer cells are present at the edge of the specimen, near healthy breast tissue.

• Negative margins indicate the edges of the specimen are clear of cancer cells.

Lymphovascular Invasion

The term "lymphovascular invasion" describes the presence of cancer cells in small blood vessels and/or lymph vessels (channels that carry lymph away from tissues). Cancer cells in blood or lymph vessels may suggest a more aggressive cancer.

Final Diagnosis

Besides noting the type of breast cancer, this part of the pathology report summarizes the key characteristics of the tumor, including cancer grade, hormone receptor status, HER2 status, and lymph node involvement.

Types of invasive breast cancer include:

• Invasive ductal carcinoma starts in the milk duct and invades into surrounding breast tissue through the milk duct wall. It may spread to lymph nodes and distant organs.

• Invasive lobular carcinoma begins in the lobules (milk glands) and spreads into nearby breast tissue and possibly beyond.

• Inflammatory breast cancer is a rare subtype of invasive ductal carcinoma. Cancer cells clog lymph vessels in the breast skin, causing breast swelling, pain, and redness.

• Triple-negative breast cancer is invasive breast cancer that is hormone receptor (estrogen and progesterone) negative and HER2-negative.

Rare types of breast cancers include:

• Paget disease of the breast begins around the breast ducts and spreads to the skin of the nipple and areola (the dark area around the nipple).

• Angiosarcomaof the breast begins in the cells that line the blood and lymph vessels.

• Phyllodes tumor begins in the breast's connective tissue and may be benign or cancerous.
  

What You Won't Find in a Pathology Report

Your cancer care team will use the pathology report to help devise a personalized treatment plan. Specific therapies, however, will not be recommended in the actual report.

Learn More: How Breast Cancer Is Treated

Summary

A breast cancer pathology report describes the features of a breast tumor and sometimes nearby tissue (e.g., lymph nodes) obtained through a biopsy or operation. These features—for example, what the cancer cells look like and whether they contain specific proteins—are intended to guide treatment decisions and determine prognosis (chance of recovery or survival).

To ensure an informed and proactive role in your cancer care, carefully review your pathology report with your oncologist (cancer doctor) or with the pathologist, and please do not hesitate to ask questions or voice concerns.

Learn More: Coping With Breast Cancer