Invasive breast cancer is a cancer that starts in the ducts or milk-producing glands of the breast and grows into the surrounding breast tissue. “Invasive” means the tumor cells have broken through the thin layer of tissue that normally keeps them inside the ducts and glands. This is what pathologists mean by invasion. Once it happens, the cancer can reach nearby lymph nodes and, less often, spread to other parts of the body, which is called metastasis.
This article explains the pathology report created after surgery to remove an invasive breast cancer, either a lumpectomy (also called an excision or partial mastectomy) or a mastectomy. It covers every item your pathologist is required to report, in roughly the order you will find them, and it applies to all types of invasive breast cancer. Reading it will help you understand what each term means and why it matters for your care.
Most pathology reports for invasive breast cancer include a section that looks like a list of headings, each followed by a short answer. This is called a synoptic report, and it follows a standard checklist published by the College of American Pathologists (CAP) and used by laboratories across North America, Europe, and much of the world. The checklist makes sure that every feature known to affect treatment decisions is reported for every patient, in the same words, no matter which laboratory examined the tissue.
One checklist covers all types of invasive breast cancer, so your report may list items that do not apply to your situation. When an item does not apply, the report will say something like “not identified,” “not applicable,” or “cannot be determined.” Seeing those phrases does not mean something was missed. It usually means the feature was looked for and was not there, or that the tissue removed did not include the structure being asked about.
The diagnosis of invasive breast cancer is made when a tissue sample is examined under a microscope by a pathologist. In almost all cases, the first sample is a core needle biopsy taken through the skin with a hollow needle, usually guided by ultrasound or mammography. Surgery follows the biopsy, and the report described in this article comes from that surgical specimen.
Under the microscope, the pathologist looks for tumor cells that have spread out of the ducts and glands into the surrounding supporting tissue of the breast. Normal ducts and glands are surrounded by a continuous layer of cells called myoepithelial cells. In invasive cancer, that layer is absent around the tumor cells. When the distinction is difficult, the pathologist may perform immunohistochemistry, a test that uses colored stains to show specific proteins in tissue. Stains for myoepithelial proteins such as p63, calponin, and smooth muscle myosin heavy chain help confirm that invasion is present, because these cells are lost around invasive tumors. A stain for a protein called E-cadherin is often used to separate the two most common types of invasive breast cancer: it is present in ductal-type tumors and absent in most lobular tumors.
After invasive breast cancer is confirmed, imaging tests are performed to assess how far the disease has spread. These may include mammography and ultrasound of both breasts and the underarm area, and in some situations MRI, CT, bone scan, or PET scan. The pathology report describes what was found in the tissue that was removed; imaging describes the rest of the body.
The first items on an invasive breast cancer pathology report describe the specimen, meaning the tissue that was sent to the laboratory, and which breast it came from.
The report may also note that lymph nodes from the underarm were removed with the breast tissue or submitted as a separate specimen.
Focality describes how many separate areas of invasive breast cancer were found in the breast. It is reported for every case.
When more than one area is found, the pathologist also describes whether the areas look the same or different. Areas with similar size, grade, type, and biomarker results are usually branches of one cancer, and the report describes them together. Areas that differ from one another are treated as separate cancers, and the report may describe each one in its own section with a label such as “Lesion 1” and “Lesion 2.” Your report may also give the number of separate areas and where they were located.
Finding more than one area of cancer does not by itself mean the cancer is more advanced. Stage is based on the largest single area, not on the total of all areas added together. What multifocal disease does affect is surgical planning, because more than one area is harder to remove completely with a lumpectomy.
Histologic type describes what the invasive breast cancer looks like under the microscope and which normal breast structure it most resembles. Pathologists assign the type using the World Health Organization (WHO) classification of breast tumors. The type contributes to the overall picture of how the cancer is likely to behave, although hormone receptor status, HER2 status, grade, and stage carry more weight in treatment decisions than type alone.
Invasive carcinoma of no special type is the most common type of invasive breast cancer, accounting for roughly 70 to 80 out of every 100 cases. It is also called invasive ductal carcinoma, and many reports use both names. “No special type” does not mean the cancer is unusual or unclassifiable. It means the tumor does not show the specific pattern required for one of the named special types below, which is the situation for most breast cancers. Under the microscope, the tumor cells form irregular nests, cords, and glands that push through the supporting tissue of the breast, and the surrounding tissue often reacts by becoming dense and scar-like. This reaction is what makes many of these tumors feel firm and show up clearly on imaging.
Some tumors of no special type show a distinctive pattern that is described but does not change the type. Your report may mention neuroendocrine differentiation, a medullary pattern (sheets of tumor cells with many immune cells around them), or another rare pattern. These descriptions are recorded alongside the type rather than instead of it.
Invasive lobular carcinoma is the second most common type, making up about 10 to 15 out of every 100 invasive breast cancers. It starts in the lobules, the small glands that produce milk. Its cells are small and uniform, and they characteristically spread through the breast in single files rather than forming a solid lump. Because of this growth pattern, lobular carcinoma can be harder to feel on examination and harder to measure on mammography, and it is more often found to be larger at surgery than imaging suggested. It is also more often multifocal and more often involves both breasts. Nearly all lobular carcinomas are hormone receptor positive.
Your report may describe the tumor as classic lobular carcinoma or as a variant pattern such as pleomorphic or histiocytoid. Pleomorphic lobular carcinoma has larger, more irregular nuclei and behaves more like a higher-grade cancer.
Some invasive breast cancers show more than one pattern. When a tumor combines ductal and lobular features, or combines a special type with no special type, the report describes it as a mixed type and gives the approximate percentage of each component. A tumor with both ductal and lobular features may also be called invasive mammary carcinoma. Treatment decisions generally follow the higher-risk component and the biomarker results.
Special types are diagnosed when at least 90 percent of the tumor shows a single distinctive pattern. Together they make up a small share of invasive breast cancers, and each of the following accounts for only about one or two out of every 100 cases or fewer.
If your tumor does not fit any listed category, the report will say “other histologic type” and describe what was seen.
Histologic grade describes how different the invasive breast cancer cells look from normal breast cells and how quickly they are dividing. All invasive breast cancers are graded using the Nottingham histologic score, also called the Elston-Ellis modification of the Scarff-Bloom-Richardson system. The pathologist scores three features from 1 to 3 and adds them together.
The three scores are added to give a total between 3 and 9, which becomes the overall grade:
Grade is one of the strongest predictors of outcome in invasive breast cancer, and it influences whether chemotherapy is considered and how genomic test results are interpreted. If the only invasive cancer found is a very small area measuring 1 millimeter or less, the report will state that grading was not performed, because there is not enough tumor to score reliably.
Tumor size is the largest measurement of the invasive breast cancer, given in millimeters. It is one of the two main factors that determine the stage of the cancer, along with the lymph nodes. The pathologist arrives at the size by combining what was seen with the naked eye, what was measured under the microscope, and what was reported on imaging.
Several rules affect how the number on your report was reached, and they explain why it may differ from the size you were told before surgery:
Ductal carcinoma in situ, usually shortened to DCIS, is a noninvasive cancer in which abnormal cells fill the ducts of the breast but have not broken through into the surrounding tissue. DCIS is found alongside invasive breast cancer in most cases, and the report describes it separately because it is measured, graded, and margin-assessed on its own. DCIS does not add to the size of the invasive tumor and does not change the stage.
Your report may include some or all of the following details about DCIS:
When breast tissue is removed for invasive breast cancer, the pathologist examines the surrounding tissue as well and reports any additional abnormal findings. None of these are cancer, and none change the stage of the invasive cancer. They matter because they are markers of increased risk in both breasts over the following years, which can influence the follow-up plan.
This part of the report describes whether the invasive breast cancer has reached structures at the front or back of the breast. It is completed only when the nipple, skin, or muscle was included in the surgery, which is usually the case for a mastectomy and often not the case for a lumpectomy. If the report says “not applicable,” those structures were either not removed or were normal and did not need to be described.
Lymphovascular invasion means that cancer cells were seen inside small blood vessels or lymphatic channels in the breast tissue outside the main tumor. These vessels are one of the routes by which invasive breast cancer reaches lymph nodes and other organs, so their involvement indicates that cells have gained access to that route. It does not mean the cancer has spread, and many patients with lymphovascular invasion have no cancer in their lymph nodes.
The report describes lymphovascular invasion as not identified, present and focal (limited to one or two vessels in a single tissue block), or present and extensive (more vessels, or vessels in more than one block). Lymphovascular invasion is associated with a higher chance of recurrence and may be taken into account when discussing radiation and systemic therapy.
If skin was removed with the specimen, the report separately states whether cancer cells were seen in the lymphatic channels of the skin. This finding, called dermal lymphovascular invasion, matters because it is the tissue change underlying inflammatory breast cancer. On its own it does not make a cancer inflammatory. That diagnosis requires the clinical findings of redness and swelling over at least a third of the breast.
Microcalcifications are tiny deposits of calcium in breast tissue. They are not cancer, and most are found in normal or benign tissue, but they show up clearly on a mammogram and are frequently the reason a breast abnormality is investigated in the first place. When calcifications were the target of the procedure, the pathologist confirms that they are present in the tissue removed and reports where they were found: in the invasive cancer, in DCIS, or in surrounding noncancerous tissue.
This item exists to confirm that the area the radiologist was concerned about was actually sampled and examined. It has no effect on stage or treatment.
Some patients receive chemotherapy, HER2-targeted therapy, or hormone-blocking therapy before surgery. This is called neoadjuvant or presurgical therapy. When it has been given, the pathologist describes how much cancer is left and how much the treatment appears to have changed it. This item is one of the strongest predictors of long-term outcome in invasive breast cancer.
The report states whether there is no known presurgical therapy, no definite response, evidence of response, or no remaining invasive cancer in the breast. When treatment has worked well, the tumor often does not simply shrink into a smaller lump. Instead, scattered small areas of cancer remain in a larger scarred area called the tumor bed, and only the largest continuous area is used for staging. When no invasive cancer remains in either the breast or the lymph nodes, this is called a pathologic complete response, and it is associated with substantially better long-term outcomes.
Reports on patients treated before surgery use the letter “y” in front of the stage, written as ypT and ypN, to show that the stage reflects the cancer after treatment rather than before it. Many reports also include the residual cancer burden (RCB), a score that combines the size of the tumor bed, the proportion of it that still contains cancer, and the amount of cancer in the lymph nodes. It is reported as a class from RCB-0 to RCB-III.
A margin is the cut edge of the tissue removed at surgery. Before examining the specimen, the pathologist coats these edges with ink so that they can be identified under the microscope, and then measures how close the invasive breast cancer and any DCIS come to the inked edge. Because invasive cancer and DCIS are managed differently, margins are reported separately for each.
For invasive breast cancer treated with lumpectomy followed by radiation, the widely used standard is “no ink on tumor,” meaning that a margin without cancer cells at the edge is considered adequate even when it is very thin. For DCIS treated the same way, a wider clearance of 2 millimeters is generally used. A positive margin raises the chance that cancer cells remain in the breast, and the surgical team may discuss removing more tissue. Distance to the deep margin at the chest wall and the front margin just under the skin is interpreted differently, because there is little or no breast tissue beyond those planes to remove.
If additional tissue was taken during the same operation or at a second operation, the final margin status takes those extra specimens into account, which is why the final statement on your report may differ from an earlier one.
Lymph nodes are small immune organs found throughout the body. Invasive breast cancer usually reaches the lymph nodes in the underarm (axilla) first, which is why these nodes are examined at surgery. Whether cancer is found in them is the single most important factor in staging invasive breast cancer.
Most patients have a sentinel lymph node biopsy, in which a dye or a radioactive tracer identifies the first few nodes that drain the breast, and only those are removed. If cancer is found in enough of them, or if nodes were known to be involved before surgery, a larger operation called an axillary dissection may be performed to remove more nodes.
Your report will include:
Deposits of cancer in a lymph node are grouped by size, and the groups are treated very differently:
Finding cancer in a small number of nodes does not automatically mean more surgery. Current practice allows many patients with one or two involved sentinel nodes who are having a lumpectomy with radiation to avoid a full axillary dissection, and your surgical team can explain how this applies to your situation.
Pathologic stage summarizes how far the invasive breast cancer had spread at the time of surgery. It is described using the TNM system from the American Joint Committee on Cancer (AJCC), 8th edition, where T describes the size and extent of the tumor, N describes the lymph nodes, and M describes spread to distant organs. The letter “p” in front means the category was determined by examining tissue under the microscope. M is almost always determined by imaging rather than by the pathologist, so most reports leave it blank or mark it not applicable.
The pathologic stage on your report is not the same thing as the overall stage group (stage I through IV) that your oncologist will discuss with you. For invasive breast cancer, that stage group also incorporates grade, estrogen receptor, progesterone receptor, and HER2 results, and it is assigned by the treating physician rather than by the pathologist.
The tumor stage for invasive breast cancer is based on the size of the largest invasive tumor and, in a small number of cases, on growth into the chest wall or skin.
Two additional labels may appear. The letter “m” in brackets means more than one separate tumor was present. The letters “pTis” mean that only in situ cancer was found, which after presurgical treatment indicates that all of the invasive cancer is gone.
The nodal stage is based on how many lymph nodes contain cancer and how large the deposits are.
The label “(sn)” after the nodal stage means the stage was based on a sentinel lymph node biopsy in which fewer than six nodes were removed.
Biomarker testing is part of the workup of every invasive breast cancer. These tests measure specific proteins and genes in the tumor and determine which treatments are likely to work. They are usually performed on the original needle biopsy, and the results are often repeated in the surgical report for completeness. If the results appear in the section of your report labeled “special studies” or “prior biomarker results,” they came from an earlier specimen, and the report will say which one.
The estrogen receptor (ER) and progesterone receptor (PR) are proteins that allow breast cells to respond to the hormones estrogen and progesterone. When a breast cancer carries these receptors, its growth is driven in part by hormones, and blocking them slows the cancer. Both are tested by immunohistochemistry and reported as the percentage of tumor cells with staining in the nucleus.
HER2 is a protein on the surface of breast cells that signals them to grow. Some invasive breast cancers make far too much of it, usually because the tumor carries extra copies of the HER2 gene, and these cancers grow faster but respond to drugs that target HER2 directly. Testing begins with immunohistochemistry, which is scored from 0 to 3+. Equivocal results go on to in situ hybridization, which counts the actual copies of the gene.
The reason your report distinguishes between complete absence of staining and faint staining is that this line now separates two groups with different treatment options, which was not the case a few years ago.
Ki-67 is a protein found only in cells that are actively dividing. It is measured by immunohistochemistry and reported as the percentage of tumor cells that show staining, so a higher number means a faster-growing invasive breast cancer. Ki-67 is used alongside grade, stage, and receptor status rather than on its own, and laboratories differ in how they measure it, so results are not always directly comparable between reports.
Genomic tests measure the activity of a panel of genes in the tumor to estimate the risk that an invasive breast cancer will return and how much benefit chemotherapy would add. They are used mainly in hormone receptor positive, HER2 negative cancers, where the decision about chemotherapy is often finely balanced. The available tests include the 21-gene recurrence score (Oncotype DX), the 70-gene signature (MammaPrint), and the 50-gene assay (Prosigna). These tests are performed at specialized laboratories on the tissue already in storage, so the result usually arrives separately, days or weeks after the pathology report.
PD-L1 is a protein that some tumors use to switch off the immune cells that would otherwise attack them. Testing for it is limited to triple negative breast cancer, meaning cancers that are ER negative, PR negative, and HER2 negative. It is measured by immunohistochemistry and reported as a combined positive score (CPS). A score of 10 or higher indicates eligibility for the immunotherapy drug pembrolizumab in advanced or metastatic disease. In early-stage triple negative breast cancer treated before surgery, immunotherapy is used regardless of the PD-L1 result, so the test is not required in that setting.
These genes control signals that tell breast cancer cells to grow, or in the case of ESR1, the estrogen receptor itself. Changes in them are usually tested by sequencing the tumor or, for ESR1, a blood sample, and testing is generally reserved for hormone receptor positive cancers that have spread or have stopped responding to hormone-blocking therapy. A change in PIK3CA, AKT1, or PTEN indicates eligibility for drugs such as alpelisib or capivasertib. A change in ESR1 explains resistance to some hormone therapies and indicates eligibility for elacestrant. These changes are usually acquired by the tumor during life and are not inherited.
BRCA1 and BRCA2 are genes that repair damaged DNA. People who inherit a faulty copy have a substantially higher lifetime risk of breast and ovarian cancer, and their tumors respond to a class of drugs called PARP inhibitors. Testing for an inherited change requires a separate blood or saliva sample, not the tumor tissue, and is arranged through a genetics service. Guidelines now offer this testing to a wide group of patients with breast cancer, including anyone diagnosed at a young age, anyone with triple negative breast cancer, anyone with a significant family history, and any man with breast cancer.
You can read more about the tests described here in the Biomarkers and Genetic Testing section of this website.
Prognosis is the expected course of a disease. For invasive breast cancer, the outlook is generally favorable, and it has improved steadily over the past three decades as screening has found cancers earlier and treatment has improved. Across all stages combined, roughly 90 out of every 100 women diagnosed with invasive breast cancer are alive five years later. When the cancer is confined to the breast, that figure is about 99 out of 100. When it has reached nearby lymph nodes, it is about 86 out of 100. When it has spread to distant organs, it is closer to 30 out of 100, although this number is rising as new treatments are introduced and it varies a great deal by subtype.
These figures describe large groups of people diagnosed years ago and cannot predict what will happen to any one person. Your own outlook depends on the combination of findings in your report, above all the following:
The pathology report for an invasive breast cancer is the document your treatment team uses to plan what comes next. Care is coordinated by a group that typically includes a surgeon, a medical oncologist, a radiation oncologist, a pathologist, and a radiologist, who often review reports together at a tumor board meeting.
The findings on your report shape several decisions:
If any part of your report is unclear, your treating physician can request the full report from the laboratory and go through it with you, and a second opinion on the pathology can be arranged if you would like one.