The pathology of lobular carcinoma in situ (LCIS) and atypical lobular hyperplasia (ALH), which are both asymptomatic and invisible to mammogram, has been a difficult problem for many years. They are now usually considered as a single category of lobular neoplasia, and increase the risk of future malignancy but may not give rise to malignancy themselves.
The true epidemiology of LCIS and ALH is difficult to quantify as the disease does not present as a distinct entity. LCIS is more common in younger women (90% of cases are pre-menopause); it is also more likely to be bilateral (about 1/3rd of cases compared with 1/6th of DCIS cases).
LCIS and ALH may be related temporally. Although the lesions increase the risk of future malignancy, they are thought to be a hallmark of pre-malignant change in the breast rather than the site of future malignancy.
Both LCIS and ALH are clinically asymptomatic and are usually invisible on mammogram. The most common means of diagnosis is during a breast biopsy for another reason.
Tumour/Normal Tissue Features
These lesions are not visible macroscopically.
LCIS is characterised by the proliferation of a monomorphic population of cells within a lobule, causing some distension of the acini but not breaching the basement membrane. Lobules are still recognisable. The cells are of low grade appearance, with smaller nuclei, minimal pleomorphism and lack of necrosis. The cells often lack cohesiveness due to loss of E-cadherin. The cells are often similar in appearance to those of invasive lobular carcinoma.
The main difference seen in ALH is that the lumen of the acini and ducts are usually preserved, with thickening of the walls caused by a mixed population of benign-appearing cells. ALH is often less extensive than LCIS.
The stage of LCIS is Tis (LCIS). ALH is not staged using TNM.
LCIS is a hallmark of future development of invasive malignancy, with a 30% risk at 20 years of developing cancer. LCIS is not thought to be the direct precursor of malignancy. ALH is thought to be earlier on the pathway to development of LCIS.