Lobular carcinoma in situ (LCIS) is an incidental microscopic finding with characteristic cellular morphology and multifocal tissue patterns.

Classic LCIS and invasive lobular lesions are low-grade ER and PR-positive cancers, referring to the positive expression of Estrogen and Progesterone receptors on the neoplastic cells (determined via immunohistochemistry).

[8] LCIS often have the same genetic alterations (such as loss of heterozygosity on chromosome 16q, the locus for the e-cadherin gene) as the adjacent area of invasive carcinoma.

Classically, LN, including LCIS, is characterized by enlargement and distension of acini making up the TDLU by proliferation of monomorphic, dyshesive, small, round, or polygonal cells with loss of polarity and inconspicuous cytoplasm.

Essentially, groups of round, almost identical looking cells that fill and expand the lobule spaces, occasionally extending into the adjacent terminal ducts – termed Pagetoid extension.

[3] This involves using marked antibodies synthetically developed to bind to target proteins expressed on or inside cells.

LCIS may be treated with close clinical follow-up (frequent scheduled checkups) and mammographic screening, tamoxifen or related hormone controlling drugs to reduce the risk of developing cancer, or, if patients and providers would like a less conservative option, bilateral prophylactic mastectomy.

[11] This is in part because multiple studies have shown no significant different in mortality due to breast cancer between women who underwent surveillance and those who elected for the mastectomy.

[13] If LCIS remains the only diagnosis after the excisional biopsy, NCCN guidelines recommend clinical follow-up every 6–12 months with annual diagnostic mammograms.

[15] Lobular neoplasia is considered pre-cancerous, and LCIS is an indicator (marker) for increased risk of developing invasive breast cancer in women.

[16] LCIS (lobular neoplasia is considered pre-cancerous) is an indicator (marker) identifying women with an increased risk of developing invasive breast cancer.

This is supported by the fact that the magnitude of increase in frequency of LCIS was greatest among women over 50 years of age (the group most likely to participate in routine mammographic screening).

In 1941, a seminal publication by Foote and Stewart introduced the term lobular carcinoma in situ, using it to categorize a spectrum of cytologic changes that were precursors to invasive cancer.

They described these changes as unrecognizable on gross examination, noninfiltrating, and multifocal, with the cells losing their apical-basal distinction (loss of polarity) and varying in shape but not size.

[19] Unlike ductal carcinoma in situ (DCIS), LCIS is not associated with calcification, and is typically an incidental finding in a biopsy performed for another reason.