New bumps or lumps on the skin can be concerning, especially if you aren’t sure whether it is a cancerous growth or a benign cyst. While it is often possible to distinguish between the two by touch and appearance, in some cases additional tests may be needed to determine which it is, says Cecilia Larocca, MD, a dermatologist and skin cancer specialist at Dana-Farber.
Cysts are sacs or pouches that can be filled with fluid, gas, or semi-solid substances. In soft tissue they are usually filled with semi-solid substances like dead skin material. No one knows what causes them. Although cysts can occur anywhere in the body, most cysts of the skin appear as rounded, raised areas, often with a pore-like opening at the top known as a punctum. They are usually moveable and feel rubbery to the hand. Cysts may occasionally drain thick, curd-like material but should not be lanced or drained at home as this may lead to inflammation or infection, and the cysts often regrow. Cysts can only be removed surgically.
A skin tumor tends to be firmer to the touch than a cyst, Larocca says, and doesn’t move if pressed, although these differences must be assessed by a trained physician.
In determining whether a skin lump is a cyst or a possible tumor, doctors may ask the patient how long the lump has been there and whether it has grown, changed color, or is painful. Lumps that don’t have the classic features of a skin cyst may be removed for testing by a pathologist to see if they are composed of cancerous or other abnormal cells. There are also numerous other benign growths that can occur under the skin aside from cysts.
Learn more about skin cancer and melanoma treatment at Dana-Farber.