No proof exists that surgery, biopsy or aspiration cause cancer to spread to distant organs.
While these procedures may sometimes cause cancer cells to be released into the bloodstream, most are incapable of establishing growth in distant organs unless they already have developed this metastatic ability. In fact, human studies suggest that the benefits of tumour sampling outweigh the risks.
For example, in a study of 2,000 people with pancreatic cancer, those who underwent sampling to obtain a diagnosis had improved outcomes compared to people who did not. The authors theorized that the information available due to the procedure helped speed appropriate cancer treatment. Local tumour spread by seeding after a biopsy procedure does occur rarely, but careful planning and good surgical technique can reduce the impact.
One example in pets is transitional cell carcinoma of the bladder, where seeding to the body wall can occur after surgery or, rarely, after needle aspiration.
Careful oncologic surgery techniques, such as changing instruments and gloves before closing the surgical wound, can reduce the seeding risk.