Lobular carcinoma in situ (LCIS) is a non-invasive neoplastic proliferation of epithelial cells within the lobules and terminal ducts of the breast. Atypical lobular hyperplasia (ALH) is diagnosed when cells similar to those seen in LCIS only partially fill the terminal duct lobular unit (TDLU) with minimal distension and distortion of the acini. LCIS and ALH are collectively referred to as lobular neoplasia. Unlike ductal carcinoma in situ (DCIS), which is usually a segmental disease in one breast, LCIS is frequently multifocal and multicentric (85% of patients) and bilateral (30-67% of patients).1
Detailed descriptions of the morphological, histological and molecular pathological characteristics of lobular neoplasia and DCIS are beyond the scope of the current document. The reader is referred to the current WHO Classification: Tumours of the Breast2 for this information. However, it should be noted that in recent years several subtypes of LCIS, in addition to the ‘classic’ variety, have been identified: ‘pleomorphic LCIS’ (PLCIS; in which cells display marked nuclear pleomorphism similar to that seen in high grade DCIS), ‘classic LCIS with comedo-type necrosis’, and ‘florid/bulky LCIS’ (classic LCIS which distends the TDLU to form confluent masses). The implications for patient management according to LCIS subtype are discussed below.
The true incidence of LCIS is unknown as the classic variant has no specific clinical or radiological features and is not seen on macroscopic examination of excisional specimens. The detection of LCIS is usually an incidental finding on core needle or excision biopsies of benign or malignant breast tissue.1 Even then, it is an infrequent finding, with an estimated prevalence of 0.4-3.8% in women with otherwise benign breast biopsies.3, 4