A breast specimen is a sample of breast tissue or cells removed for microscopic examination. This procedure, known as a biopsy, investigates breast changes like a lump or an unusual mammogram finding. The examination determines if the cells are normal, non-cancerous (benign), or cancerous (malignant), which guides any necessary next steps.
How Breast Specimens Are Collected
The collection method depends on the size and location of the concern. Fine-Needle Aspiration (FNA) uses a thin needle to withdraw a small sample of cells or fluid, often to see if a lump is a solid mass or a cyst. Because FNA collects only cells, determining if a cancer is invasive can be difficult.
A core needle biopsy (CNB) uses a larger, hollow needle to extract several small, cylinder-shaped tissue samples. This provides a more substantial sample than FNA for assessing the tissue’s structure. Radiologists often perform CNBs using imaging like ultrasound to guide the needle to the target area.
A surgical biopsy may also be performed. An incisional biopsy removes a portion of the suspicious area, while an excisional biopsy (or lumpectomy) removes the entire lump. Surgical biopsies are more invasive but provide the most comprehensive sample for analysis.
The Specimen’s Journey to the Pathology Lab
Once collected, the specimen is sent to the pathology lab. Its container is labeled with the patient’s name, an identification number, and the sample’s location. This identification is maintained throughout the process to prevent mix-ups.
The specimen is placed in a container with a preservative, usually 10% neutral buffered formalin. This fixative stops tissue decomposition. The sample should be immersed in formalin within one hour of removal to preserve cell and tissue structures for an accurate examination.
Laboratory Processing and Examination
In the lab, the specimen undergoes a “gross examination.” A pathologist or assistant inspects the tissue, documenting its size, weight, color, and texture. For a larger surgical specimen, colored inks may be applied to the outer surfaces, or margins, to orient the tissue.
Selected pieces of tissue are then placed into small plastic cassettes. These hold the tissue during processing, which involves alcohol baths to remove water, followed by a clearing agent. This prepares the tissue for embedding in paraffin wax, which forms a solid, supportive block.
The wax block is taken to a microtome, an instrument that cuts thin tissue slices about 4 to 5 microns thick. These slices are placed onto glass microscope slides. The slides are then stained with hematoxylin and eosin (H&E), a dye combination that makes cellular details visible.
Microscopic Analysis and Key Findings
Using a microscope, a pathologist examines the tissue’s cellular architecture. The goal is to identify if the tissue is benign (non-cancerous), malignant (cancer), or atypical. Atypical cells are not normal but are not yet cancerous.
The pathologist analyzes cell types, their arrangement, and their relationship to surrounding structures. For cancerous findings, the report describes the cancer type and its grade. The grade indicates how abnormal the cancer cells look and suggests the tumor’s potential growth rate.
For excisional biopsies, evaluating the surgical margins is a key part of the analysis. The ink helps the pathologist see if cancer cells extend to the edge of the removed tissue. A “negative” or “clear” margin means no cancer cells are at the edge, while a “positive” margin indicates cancer cells touch the ink.
Additional Specialized Testing
After a cancer diagnosis, further tests are performed on the tissue to guide treatment. These tests are run on the same tissue block used for the initial analysis. The goal is to identify specific characteristics of the cancer cells that can be targeted with therapy.
Hormone receptor assays determine if cancer cells have receptors for estrogen (ER) and progesterone (PR). If a cancer is ER-positive or PR-positive, hormones likely fuel its growth, and the patient may benefit from hormone-blocking therapies. About two-thirds of breast cancers are hormone receptor-positive.
Another test checks for the HER2 protein. In about 15% of breast cancers, cells make too much of this protein, causing them to grow more aggressively. This is HER2-positive breast cancer, and identifying its status is important because specific therapies can block this protein.