How Common Are False Negative Biopsies?
Biopsies take tissue samples of a suspicious area to see if cancer is present or not. The tissue sample goes to a lab for examination under a microscope. Biopsy is the main way doctors diagnose most types of cancer. Doctors biopsy to diagnose other conditions too, but the focus here is cancer biopsies.
There are several ways to take a biopsy, depending on the type of cancer and its location. Types of cancer biopsy procedures include:
Bone marrow biopsy uses a long needle to withdraw a sample of bone marrow—the spongy center of a bone. The hip bone is a common site for a bone marrow biopsy. It can show if there is cancer originating in your bone marrow, such as leukemia or lymphoma.
Endoscopic biopsy uses an endoscope to take a tissue sample from inside your body. This instrument is a thin lighted tube with a camera on the end of it. Your doctor can view the area while taking the sample. Doctors use endoscopes to take samples from the lungs, urinary tract, digestive tract, or female reproductive tract. Doctors can also insert an endoscope through a small incision in your skin to access an internal area.
Needle biopsy uses a needle to take a tissue sample from tumors. The needle can be thin for a fine needle biopsy or larger to take a core of tissue. Doctors commonly use needle biopsy when you can feel lumps through the skin or locate them with imaging equipment. Examples include a breast biopsy and lymph node biopsies.
Skin biopsy takes a sample of tissue from the surface of your skin or from deeper layers. Doctors may shave off the sample, take a ‘punch’ of skin, or cut out a skin sample.
Surgical biopsy is the most invasive type of biopsy. It involves creating an incision through the skin and directly sampling a piece of tissue harboring suspicious cells.
A false negative happens when a test result indicates there is no disease present when there actually is disease. For cancer, this would mean a test or biopsy did not find cancer when, in fact, there is cancer. The test misses the cancer. This can delay diagnosis and ultimately lead to longer and more extensive treatment.
Some types of biopsy procedures are more prone to false negative results than others. In general, needle biopsies have a higher risk of a false negative result than a surgical biopsy. Needle biopsies take a smaller tissue sample and may miss the cancer. However, even with needle biopsies, false negative results are not common. One study looking at nearly 1,000 core needle biopsies found a false negative result rate of 2.2%. That’s just over 2 out of 100 biopsies.
Sensitivity and specificity are two terms you may hear when talking about testing accuracy, including screening tests. Sensitivity is a measurement of a test’s true positive rate—having a positive test result when cancer is actually present. The closer this number is to 100%, the more likely it is that a positive result means you have cancer. Specificity measures a test’s true negative rate—not having cancer when the test result is negative. Again, the closer to 100%, the more likely it is that a negative result means you do not have cancer.
Research on breast cancer biopsies suggests that adding image guidance improves the sensitivity and specificity of core needle biopsies. Image guidance means using ultrasound or another imaging technique to locate the suspicious area and guide the needle directly into the mass of tissue. In women at average risk of breast cancer, image guidance with core needle biopsy makes the sensitivity and specificity almost equal to a surgical biopsy.
The accuracy of this method has helped core needle biopsy gain popularity in recent years. This is good news for women who want to avoid the potential complications of a surgical procedure. However, surgical biopsy may still be the best choice for some women.
Before having a biopsy procedure, you should discuss accuracy issues with your doctor. Here are some questions you may want to ask:
Does my risk of cancer affect which biopsy technique you will use?
What are the limitations of the type of biopsy you are recommending?
How will you know if you got enough tissue for the biopsy to be accurate?
Is the pathologist reviewing my biopsy a general pathologist or an expert in this type of cancer?
Will a second pathologist review my biopsy results?
What is the procedure for getting a second pathology opinion?
How often do you need to take a second biopsy to clarify the results?
In the end, experience often plays a key role in the accuracy of cancer biopsies. This includes the experience of the doctor performing the biopsy and of the lab staff preparing and evaluating the sample. If you are facing a cancer biopsy, find doctors and hospitals with plenty of experience diagnosing your potential cancer. Trust your instincts. If concerns persist after a biopsy ask that the specimen be re-examined by an expert consultant pathologist.