Mammary hamartoma was first identified by Arrigoni et al
This tumour is generally asymptomatic, with patients complaining of a lump in the symptomatic cases.2–4
The breast hamartoma is a tumour that may be underdiagnosed by pathologists because it has all the constituents of normal breast tissue.3,4
Macroscopically, it is well circumscribed.1–4
Light microscopy shows a varied combination of epithelial and stromal elements and it is easily differentiated from fibroadenoma by the presence of both lobular structures and ducts.1–4
Among mammary hamartomas previously reported in the literature, only five cases in which the hamartoma contained carcinoma have been described. Among these, two cases were lobular carcinomas and two cases were ductal carcinomas.5–7
Recently, Mester et al
reported a case with both ductal and lobular carcinomas.8
The age (mean, 45 years) of patients with hamartoma with carcinoma is generally lower than that (mean, 60 years) of patients with usual hamartomas.2,5–8
In cases where it is difficult to distinguish whether the breast carcinoma is ductal or lobular, immunohistochemical tests using antibodies against β-catenin or E-cadherin can be useful.9
The proliferation of carcinoma mainly in the lobules and the negative reaction of neoplastic cells for β-catenin as seen in our present case confirms a diagnosis of lobular carcinoma.
In conclusion, we report here a rare case of lobular carcinoma showing intraductal spread arising in a mammary hamartoma. Despite the apparent rarity of such a lesion, pathologists should be aware of the possibility of carcinomas arising within mammary hamartomas. Furthermore, we would like to emphasise the importance of careful macroscopic and microscopic examination of breast tumours to enable the presence of extremely small carcinomas to be determined, even in the more unusual cases such as mammary hamartomas.
Take home messages
- Although rare, carcinomas can arise within mammary hamartomas
- Careful macroscopic and microscopic examination of breast tumours should be undertaken to enable the presence of very small carcinomas to be determined