Phyllodes tumors also spelled phylloides and pronounced full-oy-deez) are rare breast tumors that, like fibroadenomas, contain 2 types of breast tissue: stromal (connective) tissue and glandular (lobule and duct) tissue. They are most common in women in their 30s and 40s, but they may be found in women of any age.
The tumors are usually felt as a painless lump, but some may be painful. They may grow quickly and stretch the skin. They are often hard to tell from fibroadenomas on imaging tests, or even with certain types of biopsy (the kind where a needle is used to remove a sample of tissue to look at under a microscope).
Often the entire tumor needs to be removed to know for certain that it is a phyllodes tumor.
When seen under a microscope, the main difference between phyllodes tumors and fibroadenomas is that phyllodes tumors have an overgrowth of connective tissue, and this is why a larger biopsy size is needed. The cells that make up the connective tissue part can look abnormal under the microscope. Depending on how the cells look, phyllodes tumors may be classified as benign (non-cancerous), malignant (cancerous), or borderline (looking more abnormal than benign tumors, but not quite malignant). These types of tumors can behave differently.
Phyllodes tumors (even benign ones) can sometimes come back in the same place if they are removed without taking enough of the normal tissue around them. For this reason, they are treated by removing the tumor and at least a 1 cm (a little less than ½ inch) area of normal breast tissue around the tumor.
Malignant phyllodes tumors are treated by removing them along with a wider margin of normal tissue, or by mastectomy (removing the entire breast) if needed. Malignant phyllodes tumors are different from the more common types of breast cancer, as they do not respond to hormone therapy and are less likely than most breast cancers to respond to radiation and chemotherapy drugs normally used for breast cancer. Phyllodes tumors that have spread to distant areas are often treated more like soft tissue cancer than breast cancer.
Link to cancer risk
Phyllodes tumors are usually not cancer but in rare cases they may be. Although as many as a third of these tumors are classified as malignant based on how they look under the microscope, less than 5% of phyllodes tumors overall are clearly true cancers based on spread to other areas, such as the lungs, either when they are diagnosed or later on.
Because these tumors can come back, close follow-up with frequent breast exams and imaging tests are usually recommended after treatment.