Most Common Pathology of a Lobulated Breast Mass
The most common pathology of a lobulated breast mass is fibroadenoma, which is the second most common benign breast tumor in young women under 35 years of age. 1
Characteristics of Fibroadenomas
- Fibroadenomas are well-circumscribed, hard, oval, movable lesions that typically grow up to 2-3 cm and then stop growing 2
- They can be solitary, multiple, unilateral, or bilateral and are hormone-dependent, changing consistency during menstrual cycle and pregnancy 2
- Histologically, fibroadenomas can be classified into two main types: pericanalicular and intracanalicular 2
- They can be further categorized as simple or complex fibroadenomas, with complex fibroadenomas containing cysts (3 mm), sclerosing adenosis, epithelial calcifications, or papillary apocrine changes 3
Imaging Features of Fibroadenomas
- On ultrasound, fibroadenomas most commonly appear as hypoechoic masses with circumscribed borders (57.8%) 1
- Other ultrasound features may include:
- On mammography, fibroadenomas may present with eccentric popcorn-like calcifications, particularly in older lesions 3
Clinical Significance and Management
- Most fibroadenomas (75%) are clinically palpable, while 25% are non-palpable and diagnosed with mammography and ultrasound 3
- Differential diagnosis with well-differentiated breast cancer is often necessary, particularly with medullary or mucinous tumors 3
- Excision biopsy based solely on size criteria is not warranted in clinically and radiologically concordant cases with a diagnosis of fibroadenoma on core needle biopsy 4
- In patients older than 40 years with a family history of breast cancer, lumpectomy with follow-up may be preferred to avoid the risk of underestimating in situ foci within the lump 3
Malignant Transformation and Related Pathologies
- Carcinoma arising within a fibroadenoma is rare, with an estimated incidence of 0.1-0.3% 3
- When malignancy develops within fibroadenomas, ductal carcinoma in situ is more common than lobular carcinoma in situ 5
- Phyllodes tumors represent another important differential diagnosis that shares a common origin with fibroadenomas but exhibits different growth patterns and biological behavior 2
- Unlike fibroadenomas, phyllodes tumors grow continuously and can reach sizes up to 40 cm 2
- Phyllodes tumors have a perforated capsule with finger-like projections and show higher proliferative activity (PCNA, Ki-67) compared to fibroadenomas 2
Important Considerations for Evaluation
- When evaluating a lobulated breast mass, it's crucial to consider patient age, family history, and imaging characteristics 3
- Core needle biopsy is typically sufficient for diagnosis when clinical and radiological features are concordant with fibroadenoma 4
- Surgical excision should be considered when there are cellular fibroepithelial lesions or features concerning for phyllodes tumor 4
- Adequate follow-up is essential, particularly in cases with atypical features or in patients with increased risk factors for breast cancer 3