From time to time in the history of cancer and biopsies, concern arises that biopsies and fine needle aspirates spread tumors.
Like all things medical, the truth is there are always two sides of the coin. Here, we present the bottom line information on fine needle aspirates and tumor spread in loved dogs.
When we perform a fine needle aspirate, we insert a needle and aspirate (suck) cells out. We remove the needle, which leaves a tiny tract (a tunnel) where the needle was. The cells are next placed on a slide to see if they are cancerous.
So do cancer cells move out of the hole we made with the needle and implant themselves along this tract?
For tumors under the skin, or in the skin, the benefit of a diagnosis far outweighs cancer spread risk. Fine needle aspirate is almost always a good idea.
For tumors within the abdominal cavity or pericardium (heart sac) that are filled with fluid, we must be cautious that the growths do not leak fluid with cancer cells through the tract. One can tell if a mass is fluid filled with the ultrasound. The argument to avoid fine needle aspirates in these cases is reasonable, but this is a judgement call that should be left to the vet.
For solid tumors within the body, there is very low risk of spread along the needle tract (almost always smart to get a specimen for fine needle aspirate with these)…except in the urinary tract.
For growths of the urinary tract (bladder, urethral or prostate), which in the dog are often transitional cell carcinomas, there are reports of cancer spread along the needle tract of a fine needle aspirate. Again, the argument to avoid these in general has merit. These can be often be tested using a catheter to collect the specimen as a first step, as opposed to fine needle aspirate. Again, discuss this with your veterinarian.
There is a report of a lung tumor that spread along the needle tract in the dog, but this is only a single report, and thus we need more data before suggesting we avoid fine needle aspirate for lung tumors or solid tumors in the chest cavity.
Sometimes a diagnosis can be reached by taking a piece of tissue for biopsy. This is different as a larger amount of tumor is removed compared to fine needle aspiration.
At this time, we don’t have enough data to suggest that in the dog doing surgical biopsies causes distant spread of cancers. This may change later, time will tell. There are some tumors in other species where biopsy does increase tumor spread odds, but very slightly. For more general information about this topic, this abstract has some good data. The scale tips most definitely in the direction of the biopsy.