The difference between a cyst and a polyp is that the polyp is more likely to be cancerous than a cyst is although even a polyp may not be cancerous and if removed in time they won't or should not cause any cancer.
Also a cyst is a cavity that is filled with fluid, air or semi-solid substance and and has the ability to grow and develop in any part of the body including organs.
A Polyp is basically an abnormal growth of tissue protruding from the mucous membrane and has a higher chance of developing into cancer if not removed.
A cyst can be seen on an ultrasound.
The ultrasound is a good way to see and look for a cyst and the ultrasound for the cyst can also show whether a lump is hollow, fluid-filled, or a collection of cells.
However there may need to be more tests done to determine if a cyst is cancerous or not although the good news is that most cysts are harmless and non cancerous.
When you have a cyst and need to have the cyst tested for being cancerous or not the doctor will do a biopsy either through a needle biopsy or through surgery.
Surgery is the most common way of telling if the cyst is cancerous or not.
The surgery to test if a cyst is cancerous or not involves surgically removing some or all of the lump.
Then that lump is examined and then the test results come back within a day or a few days once the test can be done.