A breast biopsy is a procedure in which a small amount of tissue is removed from the breast and sent to a pathology laboratory for examination. It is the only way to know for certain whether a breast abnormality is cancerous, precancerous, or benign. If you have received a breast biopsy pathology report, you may be finding it difficult to understand — breast reports contain a wide range of possible findings and a great deal of specialized terminology. This article explains how breast biopsies are performed, what the laboratory does with the tissue, and what the findings in your report mean.
Why is a breast biopsy done?
A breast biopsy is recommended when an abnormality is found that cannot be confidently explained by imaging alone. The most common reasons include:
- An abnormal mammogram. Mammography is the most common way to detect breast abnormalities. Findings that may prompt a biopsy include a mass, an area of architectural distortion, or microcalcifications — tiny calcium deposits that can be associated with benign, precancerous, or cancerous changes.
- An abnormal finding on ultrasound or MRI. Breast ultrasound and MRI are used alongside mammography and can detect masses or other abnormalities that warrant sampling.
- A palpable lump. A lump felt during a clinical breast examination or self-examination that cannot be confidently characterized on imaging alone.
- Nipple changes. Nipple discharge, inversion, or skin changes around the nipple may prompt a biopsy to investigate for an underlying cause.
How is a breast biopsy performed?
There are several types of breast biopsy. The type used depends on the size, location, and nature of the abnormality.
- Core needle biopsy—the most common type. A hollow needle is inserted into the breast — usually under ultrasound or mammographic guidance — to remove several small cylindrical cores of tissue. It is performed under local anesthetic and takes only a few minutes. Core needle biopsy provides enough tissue for a full pathological diagnosis, including immunohistochemistry and hormone receptor testing if cancer is found.
- Vacuum-assisted biopsy. A larger-bore needle connected to a suction device that removes multiple tissue samples in a single needle insertion. It is often used for small lesions, particularly microcalcifications detected on mammography, and removes more tissue than a standard core needle biopsy. It is performed under stereotactic (mammographic) or ultrasound guidance.
- Excisional biopsy (surgical biopsy). A surgical procedure in which the entire abnormal area is removed, rather than just a sample. This is less common now that core needle biopsy is widely available. However, it is still used when needle biopsy results are inconclusive, when certain high-risk lesions are found that require complete removal to rule out something more serious, or when a lesion cannot be reached safely with a needle.
- Fine needle aspiration (FNA). A very thin needle is used to withdraw cells from a lump or cyst. FNA provides individual cells rather than a tissue core, and can confirm whether a cyst is fluid-filled and benign, or whether a mass contains cancer cells. It is less commonly used for the primary diagnosis of breast masses because it provides less tissue than core needle biopsy and cannot always distinguish invasive from non-invasive cancer.
A small clip or marker is often placed in the breast at the biopsy site during the procedure. This marks the sampled area for future reference if surgery is needed, and allows the radiologist to confirm at follow-up imaging that the biopsy targeted the correct area.
What does the pathology laboratory do with the tissue?
Once the tissue arrives at the laboratory, it is placed in a preservative called formalin. The specimen is examined with the naked eye and then processed, embedded in paraffin wax, and cut into very thin slices, which are placed on glass slides. The slides are stained with hematoxylin and eosin dye and examined under the microscope by a pathologist.
If cancer or a high-risk lesion is found, additional tests are usually ordered on the same tissue. The most important of these are immunohistochemistry tests for estrogen receptor (ER), progesterone receptor (PR), and HER2, which are essential for treatment planning. In some cases, FISH testing is also performed to confirm HER2 status.
What are the most common findings in a breast biopsy report?
Breast biopsy reports can contain a very wide range of findings. The following covers the results patients most commonly encounter, from entirely benign to precancerous to cancerous.
Benign (non-cancerous) findings
Many breast biopsies return benign results. Benign findings do not require cancer treatment, though some are associated with a modestly increased long-term risk of breast cancer and may prompt closer surveillance.
- Fibrocystic change. The most common breast finding overall. Fibrocystic change describes a combination of cyst formation, fibrous thickening, and mild overgrowth of the glandular tissue. It is extremely common, particularly in premenopausal women, and is not associated with a significantly increased cancer risk on its own.
- Fibroadenoma. A benign tumour made up of both glandular and fibrous tissue. Fibroadenomas are the most common breast mass in young women and are not cancerous. They are followed with imaging rather than requiring further surgery in most cases.
- Intraductal papilloma. A small, wart-like benign growth inside a breast duct. It can cause nipple discharge and is removed to confirm it is benign and does not contain atypical or cancerous cells. Multiple papillomas are associated with a slightly increased cancer risk.
- Usual ductal hyperplasia. An overgrowth of the normal cells lining the breast ducts. The cells appear normal or near-normal under the microscope, and this finding is associated with only a mildly increased lifetime risk of breast cancer.
- Sclerosing adenosis. A benign condition in which the lobules of the breast are enlarged and distorted by fibrous tissue. It can mimic cancer on imaging and sometimes under the microscope, but it is benign. It is associated with a mildly increased long-term cancer risk.
- Radial scar / complex sclerosing lesion. A benign growth with a characteristic star-shaped appearance on imaging that can closely mimic invasive carcinoma. Radial scars are usually excised to confirm there is no cancer within them, and their presence is associated with a modestly increased long-term cancer risk.
- Pseudoangiomatous stromal hyperplasia (PASH). A benign overgrowth of the connective tissue of the breast that creates spaces resembling blood vessels under the microscope. PASH is not cancerous and does not significantly increase cancer risk.
- Columnar cell change and columnar cell hyperplasia. Conditions in which the cells lining the breast lobules become elongated (columnar) in shape. Without atypia (cellular abnormality), these are benign findings associated with little or no increased cancer risk.
High-risk (precancerous) findings
Some biopsy findings are not cancer but indicate that a woman’s long-term risk of developing breast cancer is significantly higher than average. These are sometimes called high-risk lesions or lesions of uncertain malignant potential. When found on core needle biopsy, most require surgical excision to ensure there is no adjacent cancer that was not sampled.
- Atypical ductal hyperplasia (ADH). Cells that partially resemble those of low-grade ductal carcinoma in situ (DCIS) but do not fully meet the criteria for that diagnosis, either because the area involved is too small or the changes are insufficient. ADH is associated with a 3- to 5-fold increased lifetime risk of breast cancer. Because ADH on core biopsy is upgraded to DCIS or invasive cancer on surgical excision in a significant proportion of cases, surgical removal of the biopsy site is typically recommended.
- Atypical lobular hyperplasia (ALH) and lobular carcinoma in situ (LCIS). Conditions in which abnormal cells fill and expand the lobules of the breast without breaking out of them. Both are considered markers of increased risk — women with LCIS have an approximately 8- to 10-fold increased lifetime risk of breast cancer in either breast. Classic LCIS is managed with surveillance and risk-reduction strategies rather than immediate surgery in most cases, though certain variants (pleomorphic LCIS, florid LCIS) may be managed more aggressively.
- Flat epithelial atypia (FEA). A condition in which the cells lining the breast lobules show mild abnormality, but without the degree of changes seen in ADH. FEA is often found alongside ADH or low-grade DCIS. Its management when found alone on biopsy is evolving, but many centres recommend excision.
- Phyllodes tumour. A fibroepithelial tumour that can range from benign to borderline to malignant. All phyllodes tumours require complete surgical excision with clear margins. Even benign phyllodes tumours can recur locally if not completely removed, and malignant phyllodes tumours can spread to other organs.
Non-invasive cancer
- Ductal carcinoma in situ (DCIS). Cancer cells that are confined within the breast ducts and have not broken through the duct wall into the surrounding breast tissue. Because the cells have not invaded, DCIS cannot spread to lymph nodes or other organs in its current state. However, DCIS has the potential to progress to invasive cancer if left untreated, so it is treated with surgery — either lumpectomy or mastectomy — often followed by radiation therapy and, in hormone receptor-positive cases, hormone-blocking medication. The pathology report for DCIS describes its nuclear grade (low, intermediate, or high), whether comedonecrosis is present, and the margin status after surgical excision.
Invasive cancer
Invasive breast cancer means that cancer cells have broken through the walls of the ducts or lobules and grown into the surrounding breast tissue. Invasive cancers have the potential to spread to lymph nodes and other organs. The most common types include:
Key findings reported for invasive breast cancer.
When invasive cancer is identified on biopsy, the pathology report will include several additional details. On a core needle biopsy, some of these — such as tumour size and margin status — cannot be fully assessed and will only be reported definitively after surgical removal of the tumour. However, grade and biomarker results from the biopsy are available and essential for early treatment planning.
Nottingham histologic grade
The Nottingham grade is the standard grading system for invasive breast cancer. It scores three features — how much the tumour resembles normal gland-forming tissue (tubule formation), how abnormal the cancer cell nuclei look (nuclear pleomorphism), and how many cells are actively dividing (mitotic rate) — each on a scale of 1 to 3. The three scores are added to give a total between 3 and 9.
- Grade 1 (score 3–5). Low grade. Cells resemble normal breast tissue—slower growing and generally associated with a better outcome.
- Grade 2 (score 6–7). Intermediate grade. Cells show moderate abnormality and grow at a moderate rate.
- Grade 3 (score 8–9). High grade. Cells look very different from normal. Faster growing and more likely to spread. It may require more aggressive treatment, but it also tends to respond better to chemotherapy.
Estrogen receptor (ER) and progesterone receptor (PR)
Estrogen receptor (ER) and progesterone receptor (PR) are proteins found on the surface of some breast cancer cells that allow the cells to use the hormones estrogen and progesterone to fuel their growth. Testing for these receptors is performed on virtually every invasive breast cancer and is usually reported as:
- Positive (ER+ or PR+). The cancer cells carry the receptor. Hormone receptor-positive cancers respond well to hormone-blocking therapies such as tamoxifen or aromatase inhibitors (anastrozole, letrozole, exemestane). These treatments significantly reduce the risk of the cancer recurring. The report will also state the percentage of cells that stain positive and the intensity of staining.
- Negative (ER− or PR−). The cancer cells do not carry the receptor. Hormone-blocking therapy is not effective for hormone receptor-negative cancers.
HER2
HER2 (human epidermal growth factor receptor 2) is a protein that promotes cell growth. In some breast cancers, the HER2 gene is amplified, and the cells make too much HER2 protein. HER2 status is tested by immunohistochemistry and, when the result is borderline (2+), confirmed by FISH. The result is reported as:
- HER2-positive (3+ by IHC, or amplified by FISH). These cancers respond to HER2-targeted therapies such as trastuzumab (Herceptin), pertuzumab, and trastuzumab-deruxtecan (Enhertu).
- HER2-low (1+, or 2+ with negative FISH). These cancers have a small amount of HER2 protein but are not classically HER2-positive. Newer antibody-drug conjugates such as trastuzumab-deruxtecan are now approved for HER2-low metastatic breast cancer, making accurate reporting of this category increasingly important.
- HER2-negative (0). No detectable HER2 protein. HER2-targeted therapies are not effective.
Breast cancer subtypes based on ER, PR, and HER2
The combination of ER, PR, and HER2 results defines the molecular subtype of the breast cancer, which is one of the most important factors in treatment planning:
- Hormone receptor-positive / HER2-negative. The most common subtype. Generally treated with surgery, often radiation, hormone-blocking therapy, and sometimes chemotherapy, depending on risk.
- HER2-positive. Treated with HER2-targeted therapy combined with chemotherapy, in addition to hormone therapy if also hormone receptor-positive.
- Triple-negative (ER−, PR−, HER2−). Does not respond to hormone therapy or HER2-targeted drugs. Treated primarily with chemotherapy. BRCA1/2 mutation testing and immunotherapy may also be relevant depending on the clinical situation.
Lymphovascular invasion
Lymphovascular invasion means that cancer cells have been found inside blood vessels or lymphatic channels in the breast tissue around the tumour. Its presence indicates that cancer cells have found a route to travel to lymph nodes or other organs, potentially, and is considered a feature associated with a higher risk of recurrence.
A note on biopsy reports versus surgical excision reports
It is important to understand that a core needle biopsy samples only a small portion of the breast abnormality. The biopsy report establishes the diagnosis and provides initial information about grade and biomarkers. Still, it cannot tell your doctors the full size of the tumour, the margin status, or whether the cancer has spread to lymph nodes. These are assessed on the surgical specimen after the tumour is removed.
In some cases, the biopsy report will note that a finding is at least a certain diagnosis — for example, “at least DCIS, invasive carcinoma cannot be excluded” — meaning the small biopsy sample cannot fully characterize what is present. This is not a cause for alarm; it is an honest statement that the full picture will only be clear once the entire tumour has been removed and examined.
Questions to ask your doctor
- What was found in my breast biopsy?
- Is the finding benign, precancerous, or cancerous?
- If a high-risk lesion was found, do I need surgical excision?
- If cancer is found, is it invasive or non-invasive (DCIS)?
- What is the grade of the cancer?
- What are the ER, PR, and HER2 results, and what do they mean for my treatment?
- What subtype of breast cancer do I have?
- Was lymphovascular invasion present?
- What surgery is being recommended, and why?
- Will I need chemotherapy, radiation, hormone therapy, or HER2-targeted treatment?
- Should I be tested for BRCA1 or BRCA2 mutations?
- What is my overall prognosis?
Related articles on MyPathologyReport.com