Invasive Mammary Carcinoma: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC and Phil Williams MD FRCPC
July 3, 2026

Invasive mammary carcinoma is a general term used to describe a cancer that has grown into the breast tissue but has not yet been sorted into a more specific type of breast cancer. It is often a starting point: after further examination and testing, most invasive mammary carcinomas are reclassified as invasive ductal carcinoma (also called invasive breast carcinoma of no special type) or invasive lobular carcinoma. Some tumors show features of both types and continue to be described as invasive mammary carcinoma.

This article explains what the term means and the findings that apply to invasive mammary carcinoma regardless of subtype. Once your tumor is subclassified, the articles on invasive ductal carcinoma and invasive lobular carcinoma cover the subtype-specific details. This article will help you understand the findings in your pathology report, what each term means, and why it matters for your care.

What is invasive mammary carcinoma?

Invasive mammary carcinoma is a family of related breast cancers rather than a single disease. The word “invasive” means the cancer cells have grown out of the ducts or lobules where they began and into the surrounding breast tissue, where they can potentially spread to lymph nodes or other parts of the body. The two most common subtypes are invasive ductal carcinoma and invasive lobular carcinoma. Because the two subtypes can be treated and behave differently, pathologists usually aim to determine which type is present.

How is the diagnosis made?

The diagnosis of invasive mammary carcinoma is usually made after a small sample of the tumor is removed in a biopsy, or after the tumor is removed by surgery, and examined under the microscope by a pathologist. The pathologist first confirms that the cancer is invasive, meaning it has grown into the surrounding breast tissue.

To classify the tumor as invasive ductal or invasive lobular carcinoma, the pathologist often performs a test called immunohistochemistry (IHC) using two markers: e-cadherin and p120. E-cadherin is a protein that helps breast cells stick together. In invasive ductal carcinoma, the cells keep e-cadherin, so it appears as strong staining around the edge of each cell (membranous staining), and p120 shows the same membranous pattern. In invasive lobular carcinoma, cells lose e-cadherin, so staining is weak or absent, and p120 moves into the cell body, showing an intracytoplasmic (within the cell) pattern. This difference is what allows the pathologist to distinguish the two subtypes. The tumor is also tested for hormone receptors and HER2 (described in the biomarker section below), and breast imaging is used to measure the size and extent of the tumor and to plan treatment.

Histologic grade

Invasive mammary carcinoma is given a histologic grade using the Nottingham grading system, which describes how closely the cancer cells resemble normal breast tissue and how quickly they are growing. The grade applies to both ductal and lobular subtypes and helps predict how the tumor is likely to behave. The pathologist scores three features, each from 1 to 3:

Tubule formation — How much of the tumor forms round, gland-like structures called tubules. More tubules is scored lower.
Nuclear pleomorphism — How variable and abnormal the cell nuclei look compared with normal cells. More abnormal nuclei are scored higher.
Mitotic rate — How many cells are actively dividing, seen as mitotic figures. More dividing cells are scored higher.

The three scores are added together (total 3 to 9) to give grade 1 (score 3 to 5, low grade), grade 2 (score 6 or 7, intermediate grade), or grade 3 (score 8 or 9, high grade). A higher grade is associated with a higher risk of spread and recurrence.

Biomarker and molecular testing

Every invasive mammary carcinoma is tested for three core biomarkers: the estrogen receptor, the progesterone receptor, and HER2. Together they define the molecular subtype of the cancer and determine which treatments are likely to work. Depending on the subtype and stage, additional molecular tests may be performed; these are described in more detail in the invasive ductal carcinoma and invasive lobular carcinoma articles.

Estrogen receptor (ER) and progesterone receptor (PR)

Estrogen receptor (ER) and progesterone receptor (PR) are proteins that allow breast cancer cells to grow in response to the hormones estrogen and progesterone. They are tested by immunohistochemistry and reported as the percentage of positive cells and the staining intensity. A cancer is hormone receptor-positive when ER or PR is present in at least 1% of cells. Hormone receptor-positive cancers can be treated with hormone-blocking therapies such as tamoxifen or aromatase inhibitors, and they tend to have a favorable outlook.

HER2

HER2 is a protein that helps control cell growth. When the HER2 gene is amplified, the cells make too much HER2 protein. HER2 is tested first by immunohistochemistry (reported as 0, 1+, 2+, or 3+), with fluorescence in situ hybridization (FISH) used to settle a borderline 2+ result. A result of 3+ or FISH-amplified is HER2-positive and can be treated with HER2-targeted drugs such as trastuzumab; 1+ or 2+/FISH-negative is HER2-low, which may respond to trastuzumab-deruxtecan in the metastatic setting; and 0 is HER2-negative.

For more information, visit our Biomarkers and Genetic Testing section.

Other findings in your pathology report

In addition to grade and biomarkers, a report on invasive mammary carcinoma typically describes several other findings. These apply to both the ductal and lobular subtypes and are covered in more detail in the subtype-specific articles.

Tumor size — Used to determine the pathologic tumor stage; larger tumors are more likely to metastasize. The final size is measured after the tumor is removed at surgery.
Lymphovascular invasion — Lymphovascular invasion means cancer cells are inside small blood vessels or lymphatic channels, which raises the risk of spread. It is reported as “present” or “absent.”
Margins — A margin is the edge of the tissue removed at surgery. A negative margin means no cancer cells at the cut edge; a positive margin means some cancer may remain and may lead to more surgery or radiation.
Lymph nodes — When breast cancer spreads, it usually reaches the axillary (underarm) lymph nodes first. The report provides the number of nodes examined, the number that contain cancer, and whether extranodal extension (spread beyond the nodal capsule) is present.

Pathologic stage (pTNM)

Invasive mammary carcinoma is staged using the TNM system of the American Joint Committee on Cancer (AJCC), 8th edition, based on the tumor (T), lymph nodes (N), and distant metastasis (M). The pathologist determines the pT and pN stages from the removed tissue; the M stage is determined by imaging.

Tumor stage (pT)

pT1 — Tumor 2 cm (20 mm) or smaller. Subdivided into pT1mi (1 mm or smaller), pT1a (more than 1 mm up to 5 mm), pT1b (more than 5 mm up to 10 mm), and pT1c (more than 10 mm up to 20 mm).
pT2 — Tumor larger than 2 cm but not larger than 5 cm.
pT3 — Tumor larger than 5 cm.
pT4 — Tumor of any size that has grown into the chest wall or skin. pT4a is growth into the chest wall; pT4b is growth into the skin causing ulcers or swelling; pT4c is both; pT4d is inflammatory breast cancer.

Nodal stage (pN)

pN0 — No cancer in the lymph nodes. Isolated tumor cells only are recorded as pN0(i+).
pN1 — Cancer in 1 to 3 axillary lymph nodes, or micrometastases only (pN1mi), or spread to internal mammary sentinel nodes.
pN2 — Cancer in 4 to 9 axillary lymph nodes, or in internal mammary nodes without axillary involvement.
pN3 — Cancer in 10 or more axillary lymph nodes, in nodes below or above the collarbone, or in a combination of internal mammary and axillary nodes.

What is the prognosis for invasive mammary carcinoma?

The prognosis for invasive mammary carcinoma depends on the specific subtype, the grade, the stage, and the biomarker results. In general, outcomes are favorable when the cancer is found early and confined to the breast, and the five-year survival for cancer that has not spread beyond the breast is high. Hormone receptor-positive cancers and cancers found at a low stage tend to have the most favorable outlook, while higher-grade cancers, cancers that have spread to lymph nodes, and triple-negative cancers carry a higher risk of recurrence. Once your tumor is subclassified, the invasive ductal carcinoma and invasive lobular carcinoma articles give prognosis information specific to each subtype.

What happens after this diagnosis?

After a diagnosis of invasive mammary carcinoma, care is usually coordinated by a team that may include a breast surgeon, a medical oncologist, a radiation oncologist, and a pathologist. The pathology findings guide which options the team considers, rather than dictating a single path. Surgery removes the tumor, either by breast-conserving surgery (lumpectomy) or removal of the whole breast (mastectomy), and lymph nodes are usually sampled at the same time. Radiation therapy is often considered after breast-conserving surgery. Systemic treatment is chosen based on the biomarker results: hormone-blocking therapy for hormone receptor-positive cancers, HER2-targeted therapy for HER2-positive cancers, and chemotherapy or immunotherapy depending on stage and subtype. After treatment, follow-up includes regular examinations and imaging to watch for recurrence.

Questions to ask your doctor

Has my tumor been subclassified as invasive ductal carcinoma or invasive lobular carcinoma, or does it show features of both?
What was the tumor size and Nottingham grade?
What is the pathologic stage of my cancer (pT and pN)?
Were any lymph nodes involved, and if so, how many?
Were the surgical margins negative, and was the tumor completely removed?
Was lymphovascular invasion present?
What were my ER and PR results, and is my tumor hormone receptor-positive?
What is my HER2 status: HER2-negative, HER2-low, or HER2-positive?
Is my cancer triple-negative, and what does that mean for treatment?
Will I need a genomic test to help decide about chemotherapy?
Which treatments are appropriate based on my pathology findings, and what are the next steps?
What follow-up and imaging schedule will I need?