Liver cancer: A major review found that needle tract seeding occurred in only about 2.7% of cases.
Breast Cancer: Extensive studies involving thousands of patients show that the risk of seeding is incredibly low, and more importantly, having a biopsy needle does not decrease a patient's chance of survival or increase the likelihood of the cancer returning.
Prostate and lung cancers: Similar trends are seen here, where the diagnostic benefit is massive, and the instances of documented spread via the biopsy needle are rare anomalies rather than a common side effect.
In a 2015 study , researchers reviewed years of data and found that the overall incidence of seeding across various cancers was less than 1%. To put that in perspective, the risk of a cancer going undiagnosed or being mistreated because a biopsy wasn't performed is significantly higher and far more dangerous.
“ This study shows that doctors and patients should feel reassured that a biopsy is very safe, ” Dr. Michael Wallace says . “ We do millions of biopsies of cancer a year in the US, but one or two case studies have led to this common myth that biopsies spread cancer. ”
Why Doesn't “ Seed” Always Grow?
One might wonder: if even one cell is “seeded ” along a needle track, doesn’t that mean a new tumor will grow? Not. necessarily.
The human body is not a passive environment; It is an active, hostile place for displaced cells. Cancer cells are specialized to thrive in their specific microenvironment (the tumor). When a few cells are dislodged during a biopsy, they usually face several hurdles :
The Immune System: Our immune systems are designed to identify and destroy “out of place” or abnormal cells. A few stray cells are often cleaned up by the body's natural defenses before they can ever take root.
Lack of Blood Supply: For a cancer cell to grow into a tumor, it needs a blood supply (angiogenesis). Isolated cells dropped along a needle track rarely have the resources to establish a new colony.
Immediate Treatment: Most biopsies are followed quickly by treatment – surgery, chemotherapy, or radiation. These treatments are designed to kill cancer cells throughout the area, including any that might have been displaced during the diagnostic process.
How Doctors Minimize the Risk
Doctors follow several precautions to ensure the risk of a biopsy is next to zero. Image credit: Shutterstock
Medical professionals do not ignore the possibility of seeding; They have developed specialized techniques to prevent it. If you are undergoing a biopsy , your medical team is likely using one or more of the following safeguards:
Coaxial needles: Many doctors use a “ sleeve” or “sheath” technique. A larger hollow needle is inserted up to the edge of the tumor, and then a smaller biopsy needle is passed through that sleeve to take the sample. When the biopsy needle is pulled back, it stays inside the sleeve, ensuring the tissue sample never touches the healthy tissue along the path.
Surgical planning: When a surgeon performs a biopsy on a tumor they intend to remove later, they carefully plan the path of the needle. They often ensure the biopsy track is located in a section of tissue that will be entirely removed during the subsequent surgery. This way, even if seeding occurs, the entire area is cut out.
Fine-Needle precision: The use of smaller needles reduces the displacement of tissue, further lowering the already slim chances of cell migration.
The Greater Danger: The “Wait and See” Approach
The fear of a biopsy spreading cancer can lead to a much more dangerous outcome: avoiding the biopsy altogether. Cancer is most treatable, and often curable, when caught early. Delaying a diagnosis allows the tumor to grow naturally. Unlike the theoretical risk of a needle spreading cells, the risk of an untreated tumor spreading on its own through the lymphatic system or the bloodstream is a virtual certainty if left long enough.
Without a biopsy, doctors are “flying blind.” They cannot know if a tumor requires aggressive chemotherapy or a simple localized surgery. Using the wrong treatment because of an incomplete diagnosis can be fatal. In the world of oncology, information is the most powerful weapon a patient has. The biopsy provides that information.
