Accepting the limitations of histologically distinguishing between ALH and LCIS (i.e. a subjective assessment of the degree of involvement of the TDLU), this distinction is clinically relevant. A greater risk of subsequent invasive breast cancer is predicted by more extensive disease: women diagnosed with ALH have a relative risk 4-5 times greater than the general population, whereas women diagnosed with LCIS have a relative risk 8-10 times higher.5 ALH is not formally considered further in this document, but given the difficulty in distinguishing between ALH and LCIS, the guidance provided for LCIS might be considered relevant to ALH.
A 2% annual incidence of breast cancer has been reported recently in women with LCIS, which is higher than earlier observations of approximately 1% per year.6 However, previous studies were not necessarily undertaken according to the current WHO criteria2, and were potentially diluted by the inclusion of ALH cases. While earlier studies suggested that the risk of invasive breast cancer in women with LCIS was equal for both breasts, recent evidence suggests that the risk of breast cancer is approximately 3 times higher in the ipsilateral breast.7-9 The overall risk of invasive breast cancer associated with LCIS is similar to the risk associated with a strong family history of breast cancer. While LCIS is clearly a risk factor for the subsequent development of invasive cancer, recent molecular data show that it is also a non-obligate precursor of invasive carcinoma. There are currently no data on the natural history of the recently recognised LCIS subtypes.