Atypical lobular hyperplasia and lobular carcinoma in situ: surgical and molecular pathology.

Lobular carcinoma in situ and atypical lobular hyperplasia were first described over 50 years ago. Despite this long incubation period, the biological nature of the lesions remains controversial. They are generally regarded as 'risk indicators' of invasive cancer rather than true precursor lesions. When first described, the 'carcinoma in situ' designation implied radical treatment in the form of a mastectomy. Subsequent observation has shown that the lesions are often multifocal and bilateral. The risk to the woman of developing invasive cancer after a diagnosis of lobular carcinoma in situ is small. Hence, the lesion has increasingly been regarded as a 'hyperplastic' proliferation, which although predicting for subsequent risk of invasive cancer, does not in itself need treatment. In this review, we challenge this view and explore the developments in the understanding of this controversial entity.