Dr Peter Schoub, a radiologist, explains why different types of breast biopsies are used.
A biopsy is the taking of samples with a needle. The purpose is to get a definitive diagnosis when a patient has a lump, or when another abnormality (lesion) is found on mammogram or breast ultrasound. Although mammograms and ultrasounds are excellent at detecting abnormalities, they can’t tell us for certain whether a cancer is present.
A biopsy is essential before surgery or other treatment. The biopsy sample is sent to a pathology lab where a pathologist will determine whether cancer is present or not. They also report the type of cancer, which is essential when deciding on the best treatment approach. In general, the larger the biopsy sample, the more accurate the diagnosis.
Breast biopsies should be performed by radiologists under ultrasound or stereotactic (mammogram) guidance. By using imaging to guide us, a needle is precisely placed into the lesion ensuring representative samples.
Biopsies are performed in mammography centres and outpatient radiology departments. Local anaesthetic is used to numb the skin and underlying tissues.
A dental needle is used; a small pinch and then it’s numb. The rest of the biopsy is painless and takes about 15 minutes. A small metallic marker is left inside the lesion.
Three types of biopsies
The types of biopsies are differentiated by the needle size and the method of sample extraction.
Fine needle aspiration (FNA)
An FNA is performed with a thin hypodermic needle attached to a syringe. The needle is moved back and forth in order to suck up cells. These cells are deposited onto a glass slide and fixed with a special spray. Usually, two to four passes are made.
FNA have several drawbacks. The fine needle extracts cells only, not actual tissue. As a result, the pathologist has less to work with and definitive diagnosis is sometimes not possible. A thin needle may also miss the relevant part of a lump, resulting in a false negative result. Therefore, core biopsies are the sampling method of choice for almost all lesions. FNA is still used to sample lymph nodes under the arm if they are too deep for a core biopsy.
A core biopsy is done with a thicker (about 2,5 x the diameter of an FNA needle) hollow needle. Using a spring-loaded mechanism, a tissue sample (sliver of solid tissue) is extracted with each firing. We tend to take two to four samples at a time.
The samples are sent in formalin (solution) to the lab where the pathologist processes the sample and determines the presence and type of cancer. A detailed report shows whether it’s a hormone or non-hormone cancer (triple negative or HER-2), and if it fast- or slow-growing.
Vacuum assisted biopsy (VAB)
VAB procedures are done with the largest needles; at least 1,5 to 2 x as large as a core needle.
The needle holder is connected to a vacuum machine which allows multiple large samples to be obtained. The amount of tissue is substantially more than that obtained with a core biopsy. However, it can result in bruising, scarring and possible displacement of biopsy markers (a VAB creates a haematoma which may displace the marker).
VAB is also performed under local anaesthetic and is the method of choice when a stereotactic biopsy is performed. Stereotactic biopsies are done for lesions seen only on mammogram, most commonly for microcalcifications.
Occasionally a VAB is done under ultrasound guidance. This is appropriate when the abnormal area is diffuse (spread out) and not a defined lump.
The reason is that VAB samples a wider area, guaranteeing good representation of the lesion. Well-defined lumps (masses) should be biopsied with a core needle. When it comes to potential cancers, the intention of biopsy is to sample, not completely excise lumps.
VAB are also sometimes used for lumps within ducts and within cysts, for example, papillomas.
In summary, core biopsy are used for lumps, VAB for diffuse abnormalities e.g. microcalcifications, and FNA for difficult to access nodes.
MEET THE EXPERT – Dr Peter Schoub
Dr Peter Schoub is a radiologist at Parklane Women’s Imaging Centre. He obtained the European Diploma of Breast Imaging in 2018 and is an honorary lecturer in the department of Radiology at the University of the Witwatersrand.
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