Breast
Other nonneoplastic
Mucocele

Editorial Board Member: Gary Tozbikian, M.D.
Editor-in-Chief: Debra L. Zynger, M.D.
Cansu Karakas, M.D.

Topic Completed: 10 November 2020

Minor changes: 10 November 2020

Copyright: 2002-2020, PathologyOutlines.com, Inc.

PubMed Search: Mucocele-like lesion of breast

Cansu Karakas, M.D.
Page views in 2019: 3,277
Page views in 2020 to date: 2,733
Cite this page: Karakas C. Mucocele. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/breastmucocele.html. Accessed November 23rd, 2020.
Definition / general
  • Rare lesion characterized by dilated epithelium lined ducts filled with mucin; associated with extravasation of acellular mucin into the stroma
  • Cysts lined by flat or low cuboidal epithelium
Essential features
  • Characterized by extravasated acellular mucin in periductal stroma
  • Although there is variable associated hyperplasia of the cyst lining in mucocele-like lesions, there are no epithelial cells floating within the luminal or extravasated mucin, which is a critical finding in distinguishing mucocele-like lesions from mucinous carcinoma of the breast
  • Although originally described as a benign lesion, associations with atypical ductal hyperplasia (ADH), ductal carcinoma in situ (DCIS) and invasive carcinoma have been reported in several studies
  • Searching for atypia when a mucocele-like lesion is present is important to exclude possibility of ADH, DCIS or invasive carcinoma
  • Pure mucocele-like lesions without atypia typically have benign behavior
Terminology
  • Mucocele-like lesion (MLL), mucocele-like tumor
Epidemiology
Sites
  • Anywhere in the breast
Etiology
  • Pathogenesis is unclear but excessive mucinous secretions or ductal obstruction may be responsible
Clinical features
Diagnosis
  • Diagnosis can be made on core biopsy or surgical specimen but careful evaluation of excised tissue, multiple H&E levels and clinicopathologic correlation may be helpful to rule out in situ lesions and invasive mucinous carcinoma
Radiology description
Radiology images

Images hosted on other servers:
Microcalcifications

Microcalcifications

Ultrasound findings of mucocele-like lesion with focal atypical proliferation

Mucocele-like lesion with focal atypical proliferation

Pleomorphic calcifications

Pleomorphic calcifications

Sonogram of palpable mass showing tubular cystic structures

Palpable mass with tubular cystic structures

Prognostic factors
Case reports
Treatment
Microscopic (histologic) description
  • Cysts and dilated ducts filled with mucin
  • Mucin containing cysts that often rupture with extravasation of mucin into surrounding stroma
  • Myoepithelial cells adhere to strips of cells floating in lakes of mucin
  • Calcifications are often present
  • Epithelium lining the cysts may show typical and atypical proliferative changes including benign / flat, hyperplasia, ADH, DCIS or mucinous carcinoma
  • Microscopic examination of the entire specimen is important to rule out any atypia / malignancy
Microscopic (histologic) images

Contributed by Cansu Karakas, M.D.
Mucin filled cyst

Mucin filled cyst

Multiple cysts

Multiple cysts

Coarse calcifications

Coarse calcifications

Extravasation of mucin

Extravasation of mucin

Cytology description
  • Poorly cellular with cohesive clusters of bland cells in 2 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)
  • Most important features favoring a benign mucocele-like lesion over mucinous carcinoma on FNA are:
    • Younger patient
    • Cells arranged in cohesive monolayers
    • No significant nuclear atypia
    • Scant cellularity
    • No or rare single, intact tumor cells
  • Mucinous carcinomas are usually more cellular with more single tumor cells, 3 dimensional clusters, mild / moderate nuclear atypia and a solid mass by imaging (Cytopathology 2004;15:104, Acta Cytologica 2000;44:765)
Positive stains
Sample pathology report
  • Left breast, upper outer quadrant, core needle biopsy:
    • Mucocele-like lesion
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
  • Mucinous carcinoma:
    • Prominent luminal cell proliferation and variable number of tumor cells floating within the mucin
    • Luminal cells in mucin are not associated with myoepithelial cells
  • Nodular mucinosis:
    • Rare lesion with accumulation of stromal mucin, typically located under or adjacent to nipple
    • Can be distinguished from mucocele-like lesions by location and staining feature of mucous substance
Board review style question #1

Which of the following statements is true about mucocele-like lesions of the breast?

  1. Frequently found in a retroareolar location
  2. Mammographically they usually form a palpable mass
  3. Most of the patients are elderly
  4. Usually benign, although they can be associated with atypia or malignancy
Board review answer #1
D. Mucocele-like lesions are typically benign, although they can be associated with atypia or malignancy. Mucocele-lesions without atypia or carcinoma are benign lesions. The other statements are false. They can arise anywhere in the breast. They commonly present with calcifications with variable circumscribed mass on mammography. There is a wide range at presentation with mean age of 40.

Comment Here

Reference: Mucocele-like lesion (MLL) of breast
Board review style question #2

A 35 year old woman had a mammogram showing polymorphous, grouped microcalcifications. The histologic details of the core needle biopsy are shown in the image above. Which of the following statements are true about this entity?

  1. CK5/6 and p63 are negative
  2. Likelihood of carcinoma is very high
  3. Mucicarmine staining is negative
  4. When there is a rupture to stroma, the possibility of mucinous carcinoma must always be considered
Board review answer #2
D. When there is a rupture to stroma, the possibility of mucinous carcinoma must always be considered. A mucocele-like lesion may show CK5/6 and p63 expression and highlight the myoepithelial cells surrounding the benign cystic lining of mucocele-like lesion. Mucin in the cyst and stroma usually show strong and diffuse mucicarmine staining in mucocele-like lesion. Mucocele-like lesion without associated carcinoma is a benign lesion.

Comment Here

Reference: Mucocele-like lesion (MLL) of breast
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