A lipoma is a benign tumor composed mainly of fat tissue. Essentially it is a pocket of fat that is encapsulated by a fibrous band. Lipomas are very common and can occur in many areas of the body and most frequently appear in the gastro-intestinal tract. Lipomas of the breast are not cancerous or precancerous, and do not increase risk for breast cancer in any way. They are slow growing tumors, and are mostly found in adults between the ages of 40 and 60, but have also been known to occur in children. Breast lipomas, however, occur more commonly in post-menopausal women.
Lipomas of the breast are quite often discovered by a woman herself and brought to the attention of a family physician, who then likely initiates breast cancer screening procedures. Most breast lipomas are painless, soft to the touch, and moveable. They tend to be quite small (less than 1 cm), but can grow up to 6 or more cm in diameter. However, breast lipomas are not always clinically palpable and are only discovered through breast cancer screening mammography. Breast lipomas also tend to be solitary tumors. Most breast lipomas are small, weighing only a few grams. A breast lipomas which is larger than 5cm and weighs more than 500g is sometimes called a "giant" breast lipoma.
Breast lipomas are not always easy to diagnose right away, which can cause increased anxiety for possible breast cancer. The presense of a painless lump in an older,adult woman does have strong potential of representing breast cancer. Both mammography and ultrasound are not always able to distinguish breast lipoma from breast carcinoma, and fine needle biopsies can often lead to confusing diagnostic results, simply based on the 'random' element of which part of the lipoma was sampled. Unfortunately, excisional biopsy is a requirement to properly diagnose breast lipoma, as only about 11% of breast lipomas present in a 'classic' pattern. On average, about 25% of lipomas are underdiagnosed.
A breast lipoma is a fat cell neoplasm that started with one cell which grew and divided too much, more than its neighbors, so essentially a microscopic evaluation should consist primarily of fat cells. Histopathologic examination of breast lipomas often reveals well encapsultated nodules of mature adipocytes, typically separated by fibrovascular septae. Breast lipomas are frequently found both with and without normal epithelial cells. Unless there is evidence of atypical nuclei and cell formations, one can be assured of the benign nature of a breast lipoma.
Mammogram and breast ultrasound will typically show no suspicious features with a breast lipoma, which usually presents as a well-circumscribed, smooth or lobulated mass. They usually show on breast X-ray as a translucent or 'radiolucent' grey mass surrounded by a radio-opaque capsule. Unless it is a very large tumor, or seems to have increased in size from a previous scan, follow up evaluation in a few months would probably be a sufficient diagnostic and management approach. Most breast lipomas should have their diagnoses "suggested" by a radiologist using common sense, from what the ultrasound and mammogram show. If the imaging result suggests that its probably a lipoma, it should not be biopsied, and should just be watched over time.
There are 3 typical sonographic appearances of breast lipomas. They can be completely isoechoic to surrounding normal fat lobules, mildly hyperechoic to nearby normal fat lobules, or isoechoic when compared to adjacent fat lobules and containing numerous thin, internal echogenic septa. Sometime ultrasound can help demonstrate the 'softness' of a breast lipoma, by documenting a decrease in the anterior-posterior measurement of the breast mass with mild transducer pressure.
The most likely treatment for a breast lipoma, if there are no suspicious features on mammogram, is to leave it alone and have a follow-up clinical and mammographic evaluation in about 6 months. The decision to biopsy is usually delayed until there is some evidence of suspicious change, as both physicians and patients usually prefer not to biopsy breast lesions which are highly likely to be benign. However if a suspected breast lipoma appears to grow rapidly during the observation period, it should be surgically removed. Some research sources claim that malignant transformation my occur within a breast lipoma, but this has yet to be documented convincingly.