How to Read Your Breast Cancer Pathology Report

October 11, 2026 · Breast Cancer, Cancer Information

A doctor writes notes in a patient's chart during an appointment. — Photo: Vitaly Gariev on Unsplash

After a breast biopsy or surgery, a pathologist studies the tissue under a microscope and writes a report. That report is one of the most important documents in your care: it tells your doctors what kind of breast cancer you have and which treatments are likely to work.

It's also written for doctors, not patients, and can be hard to read. Ask for a copy, go through it with your care team, and use this guide to understand the main terms. Labs format reports differently, so yours may not include every item below.

In situ or invasive

In situ means the abnormal cells are still inside the milk duct or lobule where they started. Ductal carcinoma in situ (DCIS) is stage 0 breast cancer.
Invasive (or infiltrating) means the cancer has grown into the surrounding breast tissue, which gives it the potential to spread.

Type

The report names the type of cancer. The most common is invasive ductal carcinoma, sometimes called "invasive carcinoma of no special type." Invasive lobular carcinoma is the next most common. There are also less common types. Our page on types of breast cancer has more.

Size and grade

Size is usually given in centimeters or millimeters and is part of the cancer's stage.

Grade describes how abnormal the cancer cells look compared with normal cells:

Grade 1 (well differentiated): cells look the most like normal cells and tend to grow slowly.
Grade 2 (moderately differentiated): in between.
Grade 3 (poorly differentiated): cells look very abnormal and tend to grow faster.

Grade is different from stage. A small, early-stage cancer can be grade 3, and a larger one can be grade 1.

Hormone receptors: ER and PR

The report says whether the cancer cells have receptors for estrogen (ER) and progesterone (PR), which let these hormones fuel the cancer's growth. Results are usually given as a percentage of cells that stain positive. According to the American Cancer Society, about 3 out of 4 breast cancers have at least one of these receptors.

ER-positive or PR-positive (hormone receptor-positive) cancers can be treated with hormone therapy, medicines that block or lower estrogen.
Cancers with fewer than 1% of cells staining are called negative. Cancers with 1% to 10% are often called low positive; ask your doctor what this means for your treatment.

HER2

HER2 is a protein that helps cancer cells grow. Labs test for it in two main ways: an immunohistochemistry (IHC) test scored 0, 1+, 2+ or 3+, and, when IHC is borderline, an in situ hybridization test (ISH or FISH) that counts copies of the HER2 gene.

HER2-positive: IHC 3+, or IHC 2+ with a positive ISH test. These cancers tend to grow faster but often respond well to drugs that target HER2.
HER2-negative: IHC 0, 1+, or 2+ with a negative ISH test. Within this group, IHC 1+ or 2+ with a negative ISH test is now often called HER2-low, and IHC 0 with faint staining in up to 10% of cells is called HER2-ultralow. These newer categories matter mainly for advanced breast cancer, where some newer drugs can work.

A cancer that is negative for ER, PR and HER2 is called triple-negative, and it's treated differently. Some triple-negative cancers are also HER2-low.

Other terms you may see

Ki-67: the percentage of cancer cells that are actively dividing. Higher numbers suggest faster growth. Not every lab reports it, and doctors weigh it alongside other results.
Lymphovascular invasion: cancer cells seen in small blood or lymph vessels near the tumor, which may suggest a more aggressive cancer.
Margins (after surgery): the edges of the removed tissue. Negative or clear margins mean no cancer cells at the edge. Positive margins mean cancer reaches the edge, and more surgery may be needed. Close margins are in between.
Lymph nodes (after surgery): how many nodes were removed and how many contain cancer. Node status is a key part of staging.

Genomic tests

For some early-stage, hormone receptor-positive, HER2-negative cancers, doctors order a gene expression test, such as Oncotype DX or MammaPrint, on the tumor tissue. These tests look at the activity of a group of genes to estimate the chance the cancer will come back, and help decide whether chemotherapy is likely to add benefit to hormone therapy. Results usually come in a separate report a week or more later.

Questions to ask about your report

Is my cancer in situ or invasive, and what type is it?
What are the size, grade, ER, PR and HER2 results?
Were my margins clear? Did cancer reach any lymph nodes?
Should I have a genomic test?
Are any results borderline or still pending?
How do these results shape my treatment plan?

If anything is unclear, or a decision rests on a borderline result, it's reasonable to ask for a second pathologist to review your slides.

The bottom line

Your pathology report tells your doctors what they're treating. You don't need to master every term, but knowing your type, grade, ER, PR and HER2 status, and stage will help you follow your treatment plan and ask better questions. For a broader overview, see our guides to breast cancer diagnosis and biopsies, and our first-month checklist for people who have just been diagnosed. You can find oncologists near you in our directory.

This article is for general information and is not medical advice. Talk with your doctor about your own situation.