A biopsy is one of the most important tools in oncology. It allows physicians to obtain a sample of suspicious tissue to confirm whether cancer is present, determine its type, and analyze characteristics that may help guide treatment. For many patients, the information obtained through a biopsy directly influences decisions regarding surgery, chemotherapy, immunotherapy, or targeted therapies.
Despite its importance, a common concern surrounds this procedure: the idea that inserting a needle or manipulating a tumor could cause cancer cells to detach and spread to other parts of the body.
This concern did not arise without reason. So-called iatrogenic tumor seeding is a recognized phenomenon in the medical literature. However, acknowledging that it can occur does not mean that all biopsies spread cancer, nor does it mean that the procedure should generally be avoided. The reality is far more complex and depends on the type of tumor, its location, the technique used, and the way the procedure is planned.
A systematic review published in Frontiers in Oncology analyzed reports of tumor seeding across different medical specialties and procedures performed between 1965 and 2022. Its objective was to identify which types of medical interventions and tumor characteristics were most frequently associated with reported cases.
What exactly is tumor seeding?
Tumor seeding occurs when cells from a primary tumor are displaced during a medical procedure and subsequently implant in another location, where they may eventually develop into a secondary tumor growth.
This displacement may occur, for example, along the path traveled by a biopsy needle, near a surgical incision, at the entry site of a laparoscopic instrument, or within tissues traversed during another invasive procedure. To be considered true tumor seeding, there must be evidence that the new tumor growth is related to the original tumor.
This is different from spontaneous metastasis. In metastasis, tumor cells detach from the original cancer, enter the bloodstream or lymphatic system, and spread to other organs as part of the natural progression of the disease. In iatrogenic tumor seeding, the displacement is associated with a medical intervention.
It is also important to distinguish tumor seeding from local recurrence. A recurrence may develop because residual tumor cells remain near the original tumor, without necessarily having been transported by a needle or surgical instrument. The authors of the review note that distinguishing between these two phenomena can be difficult, and that this uncertainty limits the interpretation of some published reports.
What did the systematic review find?
The researchers reviewed 7,165 publications and ultimately included 156 studies that met their inclusion criteria. Together, these studies described 8,161 cases of tumor seeding associated with various medical specialties and procedures.
The most frequently reported techniques were needle biopsies and minimally invasive surgical procedures, such as laparoscopy. Tumors of epithelial origin, particularly carcinomas and adenocarcinomas, were the most commonly represented histological types.
At first glance, more than eight thousand reported cases may seem alarming. However, this number must be interpreted with great caution. The review compiled cases accumulated over several decades and involving numerous cancer types, countries, medical centers, and different procedural techniques.
Furthermore, the study lacked a global denominator indicating how many millions of biopsies, surgeries, and procedures were performed during the same period without tumor seeding occurring. Because of the substantial heterogeneity of the available data, the investigators were unable to calculate an overall incidence applicable to all patients.
Therefore, the 8,161 reported cases do not indicate that there is a high probability that a biopsy will cause cancer to spread. They represent published and collected cases, not an individual’s risk of experiencing this complication.
Myth: “Every biopsy can cause cancer to spread”
The available evidence does not support this claim as a general rule.
Tumor seeding is a biologically plausible and documented complication, but the review itself describes it as a rare event. The risk is not the same across all cancers or all biopsy techniques. Even within the same organ, it may vary depending on the size of the tumor, its depth, its biological aggressiveness, and the tissues that must be traversed to obtain the sample.
It should also not be assumed that the mere presence of displaced tumor cells during a procedure will inevitably result in the development of a new tumor. For a displaced cell to produce a clinically detectable lesion, it must survive outside its original location, adapt to the new tissue, evade the immune response, obtain nutrients, and begin to proliferate—a process that is far from simple.
In other words, displacing a tumor cell does not guarantee that it has the ability to establish itself and grow.
Why are needle biopsies frequently reported?
The review identified 70 publications describing 3,448 cases associated with needle biopsies. These reports came from a variety of medical specialties, including gastroenterology, general surgery, thoracic surgery, urology, dermatology, and orthopedics.
However, the fact that a technique appears frequently in published reports does not, by itself, demonstrate that it is inherently more dangerous. Needle biopsies are performed routinely throughout the world. Consequently, a technique used millions of times may accumulate more absolute reports than one performed less frequently, even if the complication itself remains uncommon.
Tumor location also matters. A biopsy needle may need to pass through different layers of skin, muscle, adipose tissue, or organs before reaching the lesion. The depth and trajectory determine how much healthy tissue comes into contact with the needle tract.
For this reason, the authors emphasize that each case should be evaluated individually, taking into account the tumor’s size, location, histology, and the extent to which the biopsy results will influence subsequent treatment.
Not all tumors are diagnosed the Same Way
For some types of cancer, imaging studies and blood biomarkers may be sufficiently characteristic to reduce the need for a biopsy before certain therapeutic decisions are made. In other cases, obtaining tissue is essential.
Some hepatobiliary teams may favor non-invasive approaches for certain solid liver lesions. In contrast, when a sarcoma is suspected, a core needle biopsy may be essential, provided that it is performed after an appropriate radiologic evaluation and that the biopsy tract is carefully planned.
This illustrates why it is inappropriate to claim that a biopsy should always be performed—or that it should always be avoided. The decision depends on the suspected disease and on how much the information obtained from the biopsy is expected to influence treatment.
For many tumors, initiating treatment without an accurate histological diagnosis may be more harmful than the uncommon risk associated with undergoing a biopsy.
What characteristics might increase the risk?
The review explored factors such as histological type, tumor grade, tumor stage, and the technique used. Carcinomas and adenocarcinomas were the most frequently represented tumors among the published reports. This may be partially related to their high prevalence in the general population, although the authors also suggest a possible predisposition of certain epithelial tumors.
Some previous studies included in the review had associated poorly differentiated tumors and invasive carcinomas with a greater potential for tumor seeding. However, when the available data were analyzed collectively, the authors found no clear relationship between tumor stage or grade and the occurrence of tumor seeding across all cancer types.
This means that there is still no simple rule to identify which tumors are more likely to produce this complication. An advanced cancer does not necessarily carry a higher risk in every context, and a localized tumor is not completely exempt either.
The risk must be interpreted within the specific characteristics of each disease and procedure.
Tumor seeding may occur months later
One important finding was the time elapsed between the medical procedure and the detection of the secondary lesion. Among the cases that reported this variable, approximately 78% were identified more than six months after the intervention.
This finding does not mean that any abnormality detected after six months should be considered tumor seeding. Rather, it suggests that, in situations regarded as high risk, follow-up should not be limited to the immediate postoperative or post-procedural period.
Extended surveillance may be beneficial for certain tumors or techniques, particularly when the medical literature has already documented a specific risk.
How can the risk be reduced?
Prevention begins with an appropriate indication. Before performing a biopsy, the medical team should determine whether the result will truly influence the diagnosis, prognosis, or treatment.
When the procedure is indicated, planning the biopsy trajectory is essential. In some diseases, the needle tract is designed so that it can later be removed during surgery. It may also be possible to avoid passing through unnecessary anatomical compartments or tissues that could complicate future surgical intervention.
The selection of the needle type, the number of needle passes, image guidance using computed tomography or ultrasound, and the experience of the physician performing the procedure may also influence procedural safety.
In certain high-risk situations, additional preventive measures may be considered. However, the review emphasizes that further research is still needed to determine which prophylactic strategies are truly effective.
Why is it still important to talk about this?
Recognizing a rare complication is not intended to generate fear, but rather to improve medical planning. The authors observed that the risk of tumor seeding is not addressed consistently across different oncology guidelines.
In their review of the NCCN and NICE guidelines, they found that the topic was discussed for some cancer types but was absent or only partially addressed for others. Therefore, they propose updating current recommendations to include a more specific assessment of tumor seeding risk and potential preventive measures.
The best medical practice is neither to ignore risks nor to exaggerate them. It is to compare those risks with the expected benefits and make individualized clinical decisions.
Figure 1. During a biopsy, a small number of tumor cells may rarely become displaced. Successful tumor seeding requires overcoming multiple biological barriers.
A biopsy should not be seen as the enemy
The appropriate question is not simply, “Can a biopsy spread cancer?” The strict answer is that tumor seeding can occur under particular circumstances, but it is a rare complication and does not represent the usual outcome of a biopsy.
When a biopsy is appropriately indicated, it can provide crucial information that cannot be obtained through imaging alone. It can distinguish between a benign and a malignant tumor, define the cancer subtype, identify relevant biomarkers, and help avoid unnecessary or inappropriate treatments.
The review does not recommend abandoning biopsies or minimally invasive procedures. Its central message is that tumor manipulation should be performed with an understanding of the potential risk, careful anatomical planning, and attention to the specific characteristics of each patient.
In oncology, avoiding a necessary biopsy may also have consequences: delaying the diagnosis, preventing accurate tumor classification, or limiting access to personalized treatments. For this reason, the decision should always be made in collaboration with a specialized medical team, carefully weighing both the diagnostic benefits and the procedure-specific risks.
Conclusion
In conclusion, the review does not demonstrate that biopsies routinely cause metastasis. Nor does it allow the calculation of a single risk rate applicable to all tumors.
Most of the studies included in the review were retrospective. This means they analyzed previously recorded information rather than prospectively following large groups of patients from before the procedure onward.
Furthermore, the rarity of this phenomenon makes it difficult to conduct controlled clinical trials. There is also the possibility of confusing true tumor seeding with local recurrence or with the natural progression of cancer.
These limitations are fundamental. An accumulation of reported cases demonstrates that a phenomenon exists, but it does not automatically establish how frequently it occurs or what the relative risk is compared with not performing the procedure.
Main reference:
Kipnis, P., Ramanathan, D., Hoehn, R., Jethwa, A. R., Karakla, D. W., Rohr, B., Sutter, C. M., Mark, J. R., Khaja, S. F., Li, S., Thuener, J., & Carroll, B. T. (2024). Tumor seeding across specialties: a systematic review. Frontiers in oncology, 14, 1464767. https://doi.org/10.3389/fonc.2024.1464767
Other references:
Nie, C., Vaska, M., Wong, J. K., Bathe, O. F., Przybojewski, S., Burak, K. W., Tang, P. A., & Congly, S. E. (2025). Tumor Seeding With Needle Biopsy of Hepatocellular Carcinoma: A Systematic Review. The American journal of gastroenterology, 120(5), 1144–1151. https://doi.org/10.14309/ajg.0000000000003210
Polyzos, S. A., & Anastasilakis, A. D. (2010). A systematic review of cases reporting needle tract seeding following thyroid fine needle biopsy. World journal of surgery, 34(4), 844–851. https://doi.org/10.1007/s00268-009-0362-2
