A phyllodes tumor is a rare type of breast growth that originates in the connective tissue, or stroma, distinguishing it from the more common forms of breast cancer that arise in the ducts or glands. This uncommon tumor accounts for less than one percent of all breast neoplasms. The name “phyllodes” is derived from the Greek word phyllon, meaning “leaf,” which describes the characteristic leaf-like pattern seen when the tumor is examined under a microscope. Unlike benign masses like fibroadenomas, phyllodes tumors have a tendency for local recurrence, even when classified as benign, requiring a specific approach to diagnosis and treatment.
Defining Characteristics and Classification
Phyllodes tumors are classified as fibroepithelial masses, containing both stromal (connective) and epithelial (lining) components, similar to fibroadenomas. The unique microscopic feature is an exaggerated intracanalicular growth pattern, where cellular stromal tissue pushes into the ductal spaces, creating the classic cleft-like and leaf-like fronds. The risk profile is determined primarily by the characteristics of the stromal cells, as the epithelial component is typically benign across all grades.
The World Health Organization (WHO) classifies these tumors into a three-tiered system: benign, borderline, and malignant. This classification is based on specific histological features:
- The degree of stromal cell overgrowth
- Cellularity (the number of cells visible)
- The presence of abnormal-looking cells (atypia)
- The rate of cell division (mitotic activity)
Benign phyllodes tumors, which make up more than half of all cases, show mildly increased stromal cellularity and a low mitotic rate. Borderline tumors exhibit features that fall between the two extremes, such as moderate cellularity and a higher mitotic count. Malignant phyllodes tumors, accounting for about a quarter of cases, display marked cellularity, significant nuclear atypia, a high mitotic rate, and an infiltrative border.
Clinical Presentation and Diagnostic Process
Phyllodes tumors typically present as a firm, palpable mass, most often in women between the ages of 40 and 50. The primary clinical feature is rapid growth, sometimes increasing noticeably in size over a few weeks or months. Although the mass is often painless, rapid enlargement can stretch the overlying skin, causing it to appear shiny or translucent.
Initial imaging, such as a mammogram or ultrasound, often cannot definitively distinguish a phyllodes tumor from a common fibroadenoma, as both appear as large, well-circumscribed, lobulated masses. A core needle biopsy is usually the next step, but it has significant limitations due to sampling error.
Because the tumor is heterogeneous, the small tissue sample taken by a core biopsy may not capture the most aggressive part. Therefore, if a core biopsy suggests a fibroadenoma but the mass is large or growing quickly, an excisional biopsy is recommended. Definitive classification as benign, borderline, or malignant requires the pathologist to analyze the entire excised specimen.
Treatment Strategies Based on Tumor Type
Surgical removal is the primary treatment for all phyllodes tumors. The goal is a wide local excision, removing the tumor along with a surrounding rim of healthy breast tissue, known as a clear margin. This clear margin is required because the risk of the tumor returning is directly linked to whether the surgical edge is free of tumor cells.
Current guidelines recommend a margin of at least one centimeter of normal tissue surrounding the tumor to significantly reduce the risk of local recurrence. Achieving this wider margin is particularly important for borderline and malignant types. If the tumor is very large, or if a clear margin cannot be achieved with breast-conserving surgery, a total mastectomy may be necessary.
Phyllodes tumors do not typically spread to the lymph nodes, so axillary lymph node removal is not routinely performed. Adjuvant therapies are generally not used for benign or borderline tumors. Radiation therapy may be considered for malignant phyllodes tumors, especially those that are large or have close margins, though its role is still being studied. Systemic chemotherapy or hormonal therapy is reserved for cases where the malignant tumor has spread to distant organs.
Understanding Recurrence and Follow-up
The primary concern following treatment is local recurrence, which exists for all three classifications but is highest for malignant tumors. The most significant factor influencing recurrence is the status of the surgical margins; tumors with positive or very close margins are far more likely to return. Recurrence is most likely to occur within the first two years after initial surgery.
A structured follow-up schedule is necessary for surveillance. This typically involves regular clinical breast examinations every six months for the first one to two years, followed by annual check-ups. Patients who underwent breast-conserving surgery also require annual breast imaging, such as a mammogram or ultrasound. Malignant tumors carry a small risk of distant metastasis, usually to the lungs or bone, which may necessitate more intensive monitoring like chest imaging.