Breast nonmalignant
Nonneoplastic changes
Mucocele-like lesion (MLL) of breast

Topic Completed: 1 April 2016

Minor changes: 22 May 2020

Copyright: 2002-2019,, Inc.

PubMed Search: Mucocele-like lesion of breast

Cansu Karakas, M.D.
Page views in 2019: 3,277
Page views in 2020 to date: 1,247
Cite this page: Karakas C. Mucocele-like lesion (MLL) of breast. website. Accessed May 30th, 2020.
Definition / general
  • Rare lesion characterized by dilated epithelium lined ducts filled with mucin, often associated with extravasation of mucin into the stroma
  • Cysts lined by flat or low cuboidal epithelium
  • Pathogenesis is unknown but excessive mucinous secretions or ductal obstruction may be responsible
Essential features
  • Characterized by extravasated acellular mucin in periductal stroma
  • Although there is variable associated hyperplasia of the cyst lining in mucocele-like lesion, there are no epithelial cells "floating" within the luminal or extravasated mucin, which is a is critical finding in distinguishing mucocele-like lesion from mucinous carcinoma of the breast
  • Although originally described as a benign lesion, associations with ADH, DCIS and invasive carcinoma have been reported in several studies
  • This finding emphasizes the importance of searching for atypia when mucocele-like lesion is present
  • Pure mucocele-like lesion without atypia typically has benign behavior
Clinical features
Radiology description
  • There is no definitive test or imaging for differentiating mucocele-like lesion from other suspicious lesions
  • Most lesions are initially identified as indeterminate calcifications on mammogram (AJR Am J Roentgenol 2006;186:1356)
  • Sonographic finding of mucocele-like lesion most commonly reported is a cystic mass (AJR Am J Roentgenol 2011;196:1424)
Prognosis and treatment
  • Mucocele-like lesion on core biopsy warrants close radiological pathological correlation
  • Pure mucocele-like lesion without atypia is usually associated with a benign outcome (Histopathology 2013;62:894)
  • Several studies have recommended close clinical followup as an alternative to surgical excision in women with a core biopsy of mucocele-like lesion without atypia and no associated mass (Am J Clin Path 2012;138:783, Ultrasonography 2015;34:133)
  • Risk of associated malignancy is much higher if atypia is present
  • Compete surgical excision recommended in certain situations where core needle biopsy reveals the presence of associated ADH / DCIS or where a mass with indistinct and irregular margins is shown by mammography or sonography (Clin Imaging 2011;35:94, Diagnostic Pathol 2011;6:29)
Gross images

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Mucin filled cysts contained DCIS

Microscopic (histologic) description
  • Microscopic examination of the entire specimen is important to rule out any atypia / malignancy
  • Mucin containing cysts that often rupture, with extravasation of mucin into surrounding stroma
  • Epithelium lining the cysts may be benign / flat, hyperplasia, ADH, DCIS or mucinous carcinoma
  • Myoepithelial cells adhere to strips of cells floating in lakes of mucin
  • Calcifications are often present
Microscopic (histologic) images

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Mucocele-like lesions

Mucocele-like tumor

With focal columnar cell hyperplasia

With ADH

Cytology description
  • Poorly cellular with cohesive clusters of bland cells in two dimensional sheets with abundant mucoid background, no / rare intact single tumor cells, no atypia if mucocele only (Am J Surg Pathol 1999;23:552, Am J Clin Pathol 1991; 95:875)
  • Excisional biopsy is necessary to confirm diagnosis (Breast Cancer 2009;16:77)
  • The most important features favoring benign MLL over mucinous carcinoma on FNA are:
    1. Younger patient
    2. Cells arranged in cohesive monolayers
    3. No significant nuclear atypia
    4. Scant cellularity
    5. No or rare single intact tumor cells
  • Mucinous carcinomas are usually more cellular with more single tumor cells, 3D clusters, mild / moderate nuclear atypia and a solid mass by imaging (Cytopathology 2004;15:104, Acta Cytologica 2000;44:765)
Differential diagnosis
  • Cystic mastopathy: associated with prominent apocrine differentiation
  • Florid duct ectasia with luminal mucin: generally contains lipid rich material within ducts with prominent foamy histiocytes, in contrast to acellular mucin seen in mucocele-like lesion
  • Mucinous carcinoma: prominent luminal cell proliferation and variable number of tumor cells "floating" within the mucin; in mucocele-like lesions, luminal mucin is devoid of epithelial cells
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