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Other invasive carcinoma subtypes, WHO classified

Mucinous

Authors: Carissa LaBoy, M.D., Kalliopi P. Siziopikou, M.D., Ph.D.

Editorial Board Member: Gary Tozbikian, M.D.

Editor-in-Chief: Debra L. Zynger, M.D.

Last author update: 23 February 2021

Last staff update: 13 August 2024

Copyright: 2002-2024, PathologyOutlines.com, Inc.

PubMed search: Mucinous carcinoma breast mass

Table of Contents

Cite this page: LaBoy C, Siziopikou KP. Mucinous. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/breastmalignantmucinous.html. Accessed December 23rd, 2024.

Definition / general

Breast neoplasm with mucinous component that comprises > 90% of tumor, usually with favorable prognosis

Essential features

Rare tumor occurring in older women
Epithelial clusters that lie within secreted mucin (type A) or large sheets of tumor cells with neuroendocrine features and mucin production (type B)
Mucinous component must be > 90% of tumor to be pure and have favorable prognosis
ER and PR hormone receptor positive and HER2 negative (luminal A subtype)

Terminology

Colloid carcinoma
Mucinoid carcinoma
Gelatinous carcinoma
Mucoid carcinoma
Mucinous adenocarcinoma

ICD coding

ICD-O: 8480/3 - mucinous adenocarcinoma
ICD-11: 2C60 - carcinoma of breast, specialized type
ICD-11: XH1S75 - mucinous adenocarcinoma

Epidemiology

< 5% of breast carcinomas have mucinous component; of these, only 2% are pure mucinous carcinoma
F > M, sixth through eighth decades

Sites

Most are unifocal and can occur in any quadrant

Pathophysiology

Occurs through ER positive pathway, though lack gains of 1q, loss of 16q and PIK3CA mutations, which are typical of low grade neoplasms (Breast 2020;49:87)
Lesions express hormone receptors while lacking HER2 and basal markers

Etiology

Multifactorial, with factors including hormones (early menarche, nulliparity or exogenous hormone use), genetics and diet

Clinical features

Imaging can vary from a well circumscribed mass (more likely to be pure) to an irregular, spiculated mass (more likely to have mixed mucinous component) (Breast 2020;49:87)
Due to potential circumscription seen on imaging, may be mistaken for benign process

Diagnosis

More often palpable mass that appears as abnormality on mammography (StatPearls: Mucinous Breast Carcinoma [Accessed 8 January 2021])

Radiology images

Contributed by Carissa LaBoy, M.D.

Mammogram of right breast

Ultrasound of left breast

Mammogram of breast mass

Mammogram of left breast

Prognostic factors

Prognosis dependent on extent of mucinous involvement; pure mucinous carcinoma has favorable prognosis with 10 year survival rate of 90.4% (Breast 2020;49:87)
No prognostic significance between type A and type B
Patients tend to have localized disease with low recurrence rate and rare involvement of axillary lymph nodes (Breast 2020;49:87)
Component of micropapillary pattern is associated with worse prognosis, with increased rate of lymph node metastasis (Breast J 2018;24:339)
Acellular mucin seen in postneoadjuvant chemotherapy specimens does not correlate with residual disease
Only when residual neoplastic epithelium is identified is the patient classified as partial response and staged with residual disease by measuring the extent of extracellular mucin (Histopathology 2018;72:965)

Case reports

25 year old woman with slow growing mass radiologically diagnosed as fibroadenoma (Int J Surg Case Rep 2018;53:58)
48 year old woman with lump in right breast (Int J Surg Case Rep 2018;42:242)
55 year old woman with large left breast mass (Cureus 2018;10:e3606)
67 year old woman with swelling of the left breast (Iran J Pathol 2015;10:231)
75 year old woman with multiple masses in the left breast (J Med Radiat Sci 2020;67:155)

Treatment

Surgical excision and adjuvant hormone therapy
Cases associated with worse prognosis, such as micropapillary variant, may warrant neoadjuvant chemotherapy (Breast J 2018;24:339, Histopathology 2018;72:965)
HER2 positivity is associated with tamoxifen resistance and should be treated with chemotherapy, anti-HER2 therapy and endocrine therapy via an aromatase inhibitor (Medicine (Baltimore) 2020;99:e20996)

Gross description

Well circumscribed mass of variable size (from < 1 cm to > 20 cm) with gelatinous cut surface

Gross images

Contributed by Mark R. Wick, M.D.

Pure mucinous carcinoma

Images hosted on other servers:

Gross mass in the breast

Microscopic (histologic) description

Clusters / nests of tumor cells with low or intermediate nuclear grade floating in pools of extracellular mucin
Mucin pools separated by fibrous septa with capillaries
Considered pure when mucinous component comprises > 90% of the tumor, which is associated with favorable prognosis
Otherwise, tumor is mixed (mucinous component comprises 50 - 90% of tumor) or has mucinous features (mucinous component comprises < 50% of tumor), both of which have less favorable prognosis
Capella type A: abundant extracellular mucin production with scattered small epithelial clusters, strips or cribriform structures floating in pools of mucin
Capella type B: large sheets of tumor cells with mucin production and neuroendocrine features
Micropapillary pattern
- Clusters of tumor cells with intermediate to high grade nuclei, occasional hobnailing and reverse polarity; more likely to be HER2 positive, which in turn has a worse prognosis (more likely to have lymph vascular space invasion and metastasis to lymph nodes) (Breast J 2018;24:339)
- PIK3CA and TP53 mutations more frequent with recurrent gains of 8q (Histopathology 2019;75:139)

Microscopic (histologic) images

Contributed by Carissa LaBoy, M.D., Mark R. Wick, M.D. and AFIP images

Type A mucinous carcinoma

Type A ER positive

Type A PR positive

Type A HER2 negative

Clusters in mucin pools

Bland epithelial cell clusters

Strips of epithelium

Type B mucinous carcinoma

Neuroendocrine
features

Grimelius stain

Virtual slides

Images hosted on other servers:

Type A, tumor clusters

Type B, neuroendocrine features

Cytology description

Small to intermediate sized cohesive groups of epithelial cells with low grade nuclei floating within pools of extracellular mucin
Mucinous carcinoma type B displays neuroendocrine differentiation in discohesive clusters with plasmacytoid cells with low grade nuclei (Cytopathology 2016;27:193)
Low cellularity coupled with bland nuclear features and potentially scant background mucin can make the FNA diagnostically challenging (Arch Pathol Lab Med 2011;135:1533)

Cytology images

Images hosted on other servers:

FNA of mucinous carcinoma

Cytology smear of mucinous carcinoma

Cytospin preparation

Colloid carcinoma

Positive stains

ER (94%), PR (80%) (Int J Surg Case Rep 2018;42:242)
MUC2
Type B: chromogranin, synaptophysin, neuron specific enolase (NSE) (Maedica (Bucur) 2015;10:14)
WT1
GATA3

Negative stains

HER2 (up to 7% are positive) (Medicine (Baltimore) 2020;99:e20996, Int J Surg Case Rep 2018;42:242)
AR often negative (Breast 2020;49:87)
MUC1 (membrane bound mucin)

Electron microscopy images

AFIP images

Cytoplasmic mucigen granules

Molecular / cytogenetics description

Categorized as luminal A with favorable prognosis
Lacks 1p gains and 16q losses and somatic mutations of PIK3CA and AKT1, which are common in other ER+, HER2- invasive breast carcinomas (J Natl Cancer Inst 2019;111:737)
More often diploid (J Natl Cancer Inst 2019;111:737)

Videos

Review of mucinous carcinoma

Sample pathology report

Left breast, needle localized lumpectomy:
- Invasive mucinous carcinoma, grade 1 (1+2+1), measuring 1.4 cm in greatest dimension (see synoptic report)
- Margins negative with invasive carcinoma > 0.5 cm from all margins

Differential diagnosis

Mucocele-like lesion:
- Ruptured cyst with detached strips of bland epithelium lined by myoepithelial cells floating within extravasated mucin
Mucinous cystadenocarcinoma:
- Cribriform, papillary or micropapillary carcinoma lining the cysts with mucin production
- ER and PR-
Invasive micropapillary carcinoma:
- Nests of tumor cells floating in spaces, mucin production absent
Metastasis:
- Correlate with clinical and radiologic history, such as colorectal, lung and gynecologic
- Expression profile dependent on origin
Solid papillary carcinoma:
- Nests of cells with neuroendocrine features, fibrovascular cores and possible mucin production; may potentially be precursor to mucinous carcinoma
Invasive ductal carcinoma, no special type, with mucinous features:
- Histologic features are those of pure mucinous carcinoma but mucinous component does not fulfill > 90% criteria
- May be initial diagnosis on core needle biopsy for pure mucinous carcinoma
- Due to limited material sampled on core needle biopsy, amount of mucinous component is more reliably assessed on excision specimen

Board review style question #1

What is the most likely hormone receptor profile of the above breast lesion?

ER+, PR+, HER2-
ER-, PR-, HER2-
ER+, PR+, HER2+
ER-, PR+, HER2+

Board review style answer #1

A. ER+, PR+, HER2-

Mucinous carcinomas are ER+, PR+ and largely HER2-, making them a luminal A lesion, which is associated with a favorable prognosis.

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Reference: Breast - Mucinous

Board review style question #2

What percentage of a breast carcinoma must have a mucinous component to be considered pure mucinous carcinoma?

75%
50 - 90%
> 90%
30%

Board review style answer #2

C. > 90%

To be considered a pure mucinous carcinoma with a favorable prognosis, the mucinous component must comprise > 90% of a breast carcinoma. If it comprises 50 - 90% of the tumor, it is termed mixed. If the mucinous component is < 50%, the tumor is termed invasive ductal carcinoma with mucinous features. The latter two diagnoses do not have as favorable a diagnosis.

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Reference: Mucinous carcinoma

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