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Lobular carcinoma in situ

  • Lesion

LCIS is an invisible, often bilateral change in the lobules found by chance; it marks a high risk of cancer in both breasts.

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What it is

Lobular carcinoma in situ is a clonal proliferation of small, discohesive cells that fill and expand the acini of lobules. The cells have lost E-cadherin, the adhesion protein encoded by CDH1. Classic LCIS does not form a mass or calcifications, so it is found incidentally in biopsies taken for something else; it is often multicentric and bilateral. It is both a risk marker and a non-obligate precursor, raising the risk of invasive carcinoma in either breast. Pleomorphic LCIS, with large atypical nuclei and necrosis, behaves more like DCIS.

Structure

  • Acini of a lobule expanded and filled with monotonous discohesive cells; the lobular outline is preserved.
  • Cells may spread along ducts beneath the luminal epithelium (pagetoid spread).
  • Myoepithelial cells remain around the expanded acini.

Step by step

  1. A luminal cell inactivates CDH1 by mutation and loss of the other allele.
  2. Without E-cadherin, cells lose adhesion and proliferate as discohesive sheets within lobules.
  3. The change arises in several lobules and both breasts, reflecting a field of risk.
  4. Some clones invade and form invasive lobular carcinoma that grows in single files.

Markers

  • E-cadherin negative
  • p120 catenin cytoplasmic
  • ER positive
  • HER2 negative (classic type)

Clinical notes

  • Found incidentally; classic LCIS is managed by surveillance and risk-reducing options rather than wide excision.
  • Patients are offered closer imaging and may receive endocrine risk-reducing therapy.

Test yourself

Think of the answer, then tap the question to see it.

Which protein is lost in LCIS and why does it matter?

E-cadherin; without it the cells are discohesive, which explains the growth pattern of LCIS and invasive lobular carcinoma.

How is classic LCIS usually found?

Incidentally, in a biopsy done for another reason, because it forms no mass or calcifications.

Which breast is at risk in a woman with LCIS?

Both breasts; the risk of invasive carcinoma rises bilaterally.

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: Breast Cancer Treatment (PDQ®)–Health Professional Version (National Cancer Institute, 2026); Genetics of Breast and Gynecologic Cancers (PDQ®)–Health Professional Version (National Cancer Institute, 2026).

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Representative model, for educational purposes only.