What's the difference between a tumor and a cyst? Could a cyst be cancerous?

Answers from Timothy J. Moynihan, M.D.

Tumors and cysts are two distinct entities.

  • Cyst. A cyst is a sac that may be filled with air, fluid or other material. A cyst can form in any part of the body, including bones, organs and soft tissues. Most cysts are noncancerous (benign).

    Some common examples of cysts include sebaceous cysts, small bumps that form just beneath the skin and ovarian cysts. It's important to note, however, that nearly all cancers are capable of producing cysts.

  • Tumor. A tumor is any abnormal mass of tissue. Like a cyst, a tumor can form in any part of the body. A tumor can be benign or cancerous (malignant).

To determine whether a cyst or tumor is benign or malignant, a sample of the affected tissue — or, in some cases, the entire suspicious area — is removed and studied under a microscope. This is known as a biopsy.

Aug. 07, 2013 See more Expert Answers