A hamartoma is a benign lesion composed of various native tissues, but growing in a disorganized way. They may occur in the breast, but are common in other areas of the body as well. It is not considered a malignant development, as it grows at the same rate as surrounding cells. Hamartomas are mostly without symptoms and are usually not even detected unless they appear on an image taken for some other reason. But, if the lump grows very large, it can cause cosmetic distortion of the breast shape, which is usually corrected by surgically removing the lump. The main concern about hamartoma is that it can present as either a palpable lump or apparent breast mass on a diagnositc X-ray, and this naturally leads to follow-up investigations to rule out possible breast cancer. There is also a slim chance that breast carcinoma can be coincidentally developing within the epithelial cells of the hamartoma, so it has to be analyzed quite carefully.
The term 'hamartoma' is most often used in the generic sense, and it indicates a tumor composed of several different types of tissue. Typically are made of varying degrees of fibrous tissue, glandular tissue, and fat tissue, but growing in an unsual location and in a somewhat disorganzed way. We often hear the term 'fibroglandular' breast tissue, which means a combination of fibrous tissue and glandular tissue supporting the breast lobules and other structures. The 'glandular' components of this tissue would be made of 'adeno' kinds of cells. The term 'lipo' refers to the fat components. So, terms like fibroadenolipoma, lipfibroadenoma, and adenolipoma are really describing a hamartoma with respect to the cells that tend to be in a majority in that particular hamartoma.
Hamartomas are in fact more prevalent among adolescent women. This may be related to imbalances in hormone levels during puberty. They also seem to grow faster during pregnancy and lactation.
On a breast X-ray the 'classic' appearance of a hamartoma will be a well circumscribed 'lucent' (see-through) area with smooth borders, consisting of both soft tissue (fibroglandular) and lipomatous (fat) elements. Sometimes it is described as looking like a 'slice of salami'. With an ultrasound a hamartoma will usually appear as a well-defined, solid, oval mass, quite similar visually to the more common fibroadenoma It will usually reveal sonolucent fat and some echogentic fibrous elements, with a heterogenous internal echo pattern. (In other words, the sonographic profile is kind of a mixed bag). MRI is sometimes employed and tends to give a clearer picture of the internal fat densities, the smooth and well-defined rim, and the heterogenous internal elements.
In terms of its microscopic appearance and histology, breast hamartoma does not really have distinctive diagnostic properties. A pathologist might note fibrous tissue within the breast lobules, or fibrous tissue and fat in the supporting stroma with or without pseudo-angiomatous changes,(relating to blood supply). Commonly, hamartomas will appear as otherwise normal-looking breast tissue, but distributed in nodules within the fibrotic stroma surronding and extending between individual breast lobules, possibly obliterating the normal 'interlobular' loose stroma. In the image of hamartoma pictured below, the histology could be decribed as having lots of fibrous tissue, with embedded islands of glandular cells, and fat around the outside (in the bottom-left).
These kind of features, when combined with X-ray and sonograph images and a clinical understanding of the age and context of the women in question, should suggest a probable diagnosis of hamartoma. It is highly unlikely that any single diagnostic approach can confidently diagnose breast hamartoma.
Breast hamartomas are benign, but, in rare instances they have been known to develop simultaneously with coincidental breast epithelial cell malignancy, within the same lesion. So, it is possible that the tumor may be too-quickly dismissed as just a hamartoma without full investigation. If there is a distinct 'lump', and if there is evidence of asymmetrical breast density on the Xray, this could suggest something more serious.
Breast hamaroma has an estimated incidence rate between 0.1 and 0.7 %, which is very low. However, as more women participate in breast cancer screening programs, and at earlier ages, the indicence rate may appear to rise. Even though they are benign, the possibility that breast carcinoma may lie undiscovered within the epithelial elements of the hamartoma will likely lead to fairly intensive biopsy sampling, and quite likely a surgical removal of the affected area.
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