A fibroepithelial lesion is a common finding, primarily within breast tissue, that requires careful evaluation because the term describes a wide range of conditions. This classification indicates an overgrowth involving two distinct types of tissue components within the breast. The spectrum of these lesions extends from growths that are extremely common and completely harmless to those that are rare and carry a potential for malignancy. Understanding the specific type of fibroepithelial lesion present is paramount, as the diagnosis directs the necessary follow-up and determines the appropriate course of action.
What Defines a Fibroepithelial Lesion
The name “fibroepithelial” defines the lesion’s composition. The “fibro” element refers to the fibrous connective tissue, known as the stroma, which provides structural support to the breast. The “epithelial” element refers to the cells that line the ducts and glands within the breast tissue. Fibroepithelial lesions are characterized by a simultaneous and coordinated proliferation of both these components.
These lesions are considered biphasic tumors because they involve the growth of two different cell lines. They arise from the terminal duct lobular unit, the functional part of the breast where milk production occurs. The degree of growth and cellularity in each component, particularly the stroma, is what pathologists use to distinguish between the different types.
Understanding the Spectrum of Lesions
The spectrum of risk is defined by two main categories: fibroadenomas and phyllodes tumors. These are differentiated by the behavior and cellularity of the stromal component. Fibroadenomas are the most frequent type of fibroepithelial lesion and are considered benign growths. They are slow-growing, often present as firm, mobile lumps, and are most common in women under the age of 30.
Fibroadenomas may be classified as simple or complex. Complex fibroadenomas contain additional features like cysts, sclerosing adenosis, or epithelial calcifications. While still benign, a complex fibroadenoma may be associated with a slightly increased risk of breast cancer compared to a simple fibroadenoma. The stromal cells in a fibroadenoma show limited cellular activity and little evidence of abnormal cell division.
Phyllodes tumors represent the other, less common end of the spectrum and carry a higher risk profile. They are rare, accounting for less than one percent of all breast tumors, and typically present in women in their 40s and 50s. The distinction from fibroadenoma is determined by the increased cellularity and overgrowth of the stromal component, which often causes the lesion to grow rapidly.
Phyllodes tumors are graded into three categories: benign, borderline, and malignant, based on five specific features seen under the microscope:
- The degree of stromal cellularity
- The presence of nuclear atypia (abnormal-looking cell nuclei)
- The number of mitotic figures (dividing cells)
- The tumor border
- The presence of stromal overgrowth
Malignant phyllodes tumors show the highest cellularity, numerous dividing cells, and have the potential to spread to other parts of the body, unlike fibroadenomas.
How Doctors Detect and Diagnose
Imaging tests like mammography and ultrasound are used initially to characterize the lesion’s physical appearance. On ultrasound, a fibroadenoma often appears as a well-circumscribed, oval, hypoechoic mass, suggesting a benign nature. Phyllodes tumors may appear larger, sometimes with an irregular shape or internal cystic spaces, though there is significant overlap in appearance between the two.
The definitive step is a tissue sampling procedure, most commonly a core needle biopsy (CNB). This procedure removes small cylinders of tissue for pathological examination. The pathologist then analyzes the tissue to assess the ratio and characteristics of the epithelial and stromal components.
If the CNB sample shows features that lie in the “gray zone” between a cellular fibroadenoma and a benign phyllodes tumor, the pathologist may be unable to make a final diagnosis. In these uncertain cases, the finding is often reported simply as a “fibroepithelial lesion.” This indicates that the entire mass needs to be surgically removed for a complete examination. Excisional biopsy is sometimes necessary to obtain enough tissue to accurately grade the stromal component and rule out a phyllodes tumor.
Management and Follow-Up Care
Simple fibroadenomas confirmed by core needle biopsy and not growing are often managed conservatively with observation and routine follow-up imaging. If a fibroadenoma is complex, symptomatic, or rapidly increasing in size, surgical excision may be recommended. This confirms the absence of a higher-risk lesion and alleviates symptoms.
All grades of phyllodes tumors—benign, borderline, and malignant—require surgical removal. Even benign phyllodes tumors have a higher risk of local recurrence if not fully excised. For borderline and malignant tumors, it is important to remove the tumor with a margin of surrounding normal tissue to reduce the risk of the tumor returning.
For patients with a phyllodes tumor, careful long-term follow-up is necessary to monitor for potential recurrence. Recurrence is the main concern following treatment. The specific follow-up schedule and imaging plan are tailored based on the final pathological grade of the excised tumor.