A breast biopsy is a procedure where a small tissue sample is removed from a suspicious area in the breast. This sample is sent to a laboratory for analysis by a pathologist, a doctor who specializes in examining tissue to diagnose diseases. The purpose of the biopsy is to determine if cancer cells are present, which is the only definitive way to confirm a breast cancer diagnosis. This process involves careful handling, sophisticated analysis, and provides a wealth of information that guides medical care.
The Tissue Sample’s Journey to the Laboratory
The journey of a breast tissue sample begins the moment it is removed. The sample is immediately preserved in a labeled container filled with formalin, a preservative solution of formaldehyde and water. This process, known as fixation, prevents the cells from degrading. It locks the cellular structures in place for an accurate examination.
Proper labeling identifies the sample with the patient’s information and the specific location it was taken from. A request form with the patient’s history accompanies the sample to provide context for the pathologist. The container is sealed in a secure transport bag and sent to a pathology laboratory. A strict chain-of-custody protocol is followed during transport.
Initial Microscopic Examination for Diagnosis
In the laboratory, the formalin-fixed tissue is processed through alcohols to remove water and then cleared with a solvent. The tissue is then infiltrated with and embedded in a block of paraffin wax. This creates a solid, stable block that allows for extremely thin slicing.
Using an instrument called a microtome, a technician cuts the paraffin block into sections a few micrometers thick. These tissue sections are floated onto a water bath and mounted onto glass microscope slides. The slides are then heated to make the tissue adhere firmly before staining, which makes cellular components visible.
The primary staining technique is the Hematoxylin and Eosin (H&E) stain. Hematoxylin stains cell nuclei purplish-blue, while eosin stains the cytoplasm and connective tissue in shades of pink. This color contrast allows a pathologist to see the tissue’s architecture and the individual characteristics of the cells. The pathologist examines the arrangement of the cells, their size, shape, and how they relate to one another.
The H&E examination allows the pathologist to make a diagnosis. They determine if the tissue is benign (non-cancerous), atypical (has abnormal features), or malignant (cancerous). If cancer is present, the pathologist identifies its type, such as ductal carcinoma in situ (DCIS) or invasive ductal carcinoma (IDC). They also assign a grade from 1 to 3, which indicates how quickly the cancer might grow based on how different the cells look from normal cells.
Essential Biomarker Analysis for Treatment Planning
After a cancer diagnosis, the tissue is tested for specific molecular characteristics called biomarkers. These tests help understand the cancer’s behavior and predict which treatments will be most effective. The analysis is performed on thin slices of tumor tissue mounted on slides.
The three primary biomarkers tested for are the Estrogen Receptor (ER), Progesterone Receptor (PR), and Human Epidermal growth factor Receptor 2 (HER2). ER and PR are proteins inside some cancer cells. A technique called immunohistochemistry (IHC) uses special antibodies that bind to these hormone receptors. If the receptors are present, a chemical reaction causes a color change visible under a microscope.
A positive result for ER or PR means the cancer uses hormones to grow. This indicates the cancer will likely respond to hormone-blocking treatments, known as endocrine therapy. These therapies work by lowering hormone levels or by blocking them from attaching to cancer cells, which slows or stops their growth.
The HER2 test determines if cancer cells have excess HER2 protein, which can cause more aggressive growth. The initial test is an IHC stain that measures the amount of HER2 protein. If the IHC results are unclear, a more definitive test called fluorescence in situ hybridization (FISH) is used. The FISH test counts the number of HER2 genes in the cancer cells for a clear result. A HER2-positive diagnosis means targeted therapies designed to attack these specific cells can be used.
Advanced Genomic and Proliferation Testing
Additional specialized tests can further refine treatment decisions, particularly regarding chemotherapy. One test measures the Ki-67 protein, which is found in actively dividing cells. The Ki-67 score is a percentage indicating how many tumor cells are proliferating. A higher Ki-67 percentage suggests a faster-growing tumor.
For certain early-stage, ER-positive, HER2-negative breast cancers, genomic assays are used. Tests like Oncotype DX and MammaPrint analyze the activity of a specific set of genes within the tumor cells. These assays examine a panel of genes related to cell growth and division to generate a recurrence score.
This score helps predict the likelihood of the cancer returning after initial treatment. It also clarifies which patients are most likely to benefit from adding chemotherapy to their hormone therapy. A low recurrence score may indicate that hormone therapy alone is sufficient, allowing a patient to avoid chemotherapy. These tests offer a more detailed risk assessment than tumor size or grade alone.
Understanding the Pathology Report and Tissue Storage
All information from the examinations is compiled into a comprehensive pathology report. This document details the final diagnosis, including the cancer type, grade, and size. It also includes the biomarker status (ER, PR, and HER2 results) and the results from any advanced genomic tests.
The report is sent from the laboratory to the patient’s surgeon or oncologist. The physician uses this information to discuss the prognosis and create a tailored treatment plan with the patient. This report guides all subsequent medical decisions.
After testing, the physical tissue samples are preserved. The paraffin wax block containing the tumor tissue, or “tumor block,” is stored in the laboratory’s archives for many years according to regulatory guidelines. This long-term storage allows the tissue to be available for a second opinion or for additional testing if new treatments become available. With patient consent, it can also be used for medical research.