Receiving a mammogram report with unfamiliar terms can be unsettling. The Breast Imaging Reporting and Data System, or BI-RADS, is a standardized tool radiologists use to communicate their findings clearly. This system categorizes results on a scale from 0 to 6. A BI-RADS 4 finding is an intermediate category that indicates a need for further evaluation. It is important to understand that this is not a cancer diagnosis but a signal that a suspicious area requires a closer look to determine its nature.
What a BI-RADS 4 Finding Means
A BI-RADS 4 assessment means a “suspicious abnormality” has been identified on an imaging test like a mammogram or ultrasound. These findings could include masses with irregular shapes or indistinct borders, or tiny calcium deposits known as microcalcifications that are arranged in a concerning pattern. Such features are not definitive for cancer but are irregular enough to raise suspicion.
The BI-RADS 4 category covers a very broad statistical range, with a likelihood of cancer anywhere from 2% to 95%. While the finding is taken seriously, many abnormalities in this category are ultimately found to be benign. In fact, only about 20-30% of BI-RADS 4 findings that are biopsied turn out to be malignant. The primary purpose of this classification is to flag an area that cannot be dismissed as benign based on imaging alone.
The Subcategories of BI-RADS 4
To provide a more precise level of suspicion, the BI-RADS 4 category is divided into three subcategories: 4A, 4B, and 4C. These classifications help to better define the radiologist’s level of concern and manage expectations for what comes next. Each subcategory corresponds to a more specific probability of malignancy, which can be helpful for both patients and their doctors.
Category 4A signifies a low suspicion for malignancy. Findings in this group have a greater than 2% but less than or equal to 10% chance of being cancerous. An abnormality might be placed in this subcategory if it has some slightly worrying features, but overall does not look highly characteristic of cancer.
A BI-RADS 4B assessment indicates a moderate suspicion for malignancy. This means there is a greater than 10% but less than or equal to 50% likelihood that the finding is cancer. A radiologist might assign this category to a lesion that has more concerning features than a 4A finding, such as more irregularity in its shape or margins.
The highest level of suspicion within the category is 4C. This designation is used for findings that have a greater than 50% but less than 95% chance of being malignant. These abnormalities have features that are very suggestive of cancer, such as a mass with a spiculated (spiky) margin.
The Recommended Biopsy Procedure
A biopsy is the standard and necessary next step for any BI-RADS 4 finding because it is the only way to obtain a definitive diagnosis. While imaging tests can identify suspicious areas, they cannot determine with certainty if cells are cancerous. By removing a small sample of the tissue in question, a specialist called a pathologist can examine the cells under a microscope and provide a clear answer.
For most BI-RADS 4 findings, a minimally invasive procedure called a core needle biopsy is the preferred method. This is an outpatient procedure performed using local anesthesia to numb the breast tissue. Guided by ultrasound, MRI, or mammography, the radiologist inserts a hollow needle into the suspicious area to remove several small, cylindrical samples of tissue. Because it is guided by imaging, it is highly accurate at targeting the correct location.
A tiny clip, which cannot be felt, may be placed in the breast to mark the biopsy site for future reference. The tissue samples are then sent to a pathology lab for analysis.
Interpreting Biopsy Results
After the biopsy, a pathologist examines the tissue and prepares a report. The results will fall into one of three main categories. The most frequent outcome for a BI-RADS 4 finding is benign, meaning the suspicious area is not cancerous. In this case, follow-up might involve returning to routine annual screening or a slightly earlier follow-up imaging exam in six months to ensure stability.
Another possible outcome is the identification of a high-risk lesion, sometimes called atypia. These cells are not cancerous, but they are abnormal and can indicate an increased risk for developing breast cancer in the future. A finding of atypical cells often requires a consultation with a surgeon to discuss surgically removing the entire area to ensure no cancer was missed and to reduce future risk.
The third potential result is a malignant diagnosis. If this is the outcome, the pathology report will provide details about the specific type of cancer. The healthcare team will then discuss the findings and outline the next steps for developing a comprehensive treatment plan.