How can you tell the difference between a lipoma from a cancer in a dog?

Lipomas are a type of cancer but they're considered to be more benign, meaning they grow as tumors (with cells behaving abnormally that can't control their growth). There are a couple of things you can do to distinguish between lipomas and other forms of cancer—one is a fine needle aspirate, where you use needles to collect a population of cells from different places within the mass. However, this method isn't always comprehensive. A better, more thorough way of doing it is taking a biopsy, which is where you sample and test a small piece of tissue.