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Immunohistochemistry in Breast Pathology - Part 1



Resolving common diagnostic dilemmas


  1. Benign/malignant e.g. Radial scar v Invasive cancer; Nipple adenoma - See also Sclerosing Lesions
  2. Epithelial proliferations e.g. ADH v DCIS - See also Carcinoma in situ and ADH & ALH
  3. In situ v microinvasion


Benign v Malignant



Myoepithelial markers are employed very frequently to help differentiate invasive from non-invasive lesions, particularly Radial Scar v Grade 1 invasive cancer; intraduct papilloma v Papillary intraduct carcinoma and ADH v DCIS.

In benign sclerosing lesions the myoepithelial layer is retained around glandular structures and therefore these can be expected to show positive staining with a marker such as CK 5/6. In low grade invasive carcinomas the myoepithelial layer is absent and CK 5/6 staining is negative.

The following images illustrate the use of IHC in these conditions:


Sclerosing lesions



Low power view of radial scar

High power view of duct with moderately severely atypical intraductal proliferation


Detail of central fibroelastotic scar with entrapped glands

High power view of duct with moderately severely atypical intraductal proliferation

Radial scar - Note - CK 5/6 shows intact myoepithelial layer throughout
Centre of scar showing crowded benign glandular elements and elastosis (stains bright pink here) Radial scar - note intact myoepithelial layer around benign glandular elements shown by CK 5/6 immunostaining


Low power view of core biopsy showing sclerosing adenosis and adjacent invasive carcinoma.
'Mouse over' - Green circle = sclerosing adenosis; yellow ellipse = area of invasive carcinoma

Low power view of core biopsy - Green circle = sclerosing adenosis; yellow ellipse = area of invasive carcinoma

Detail of above image
'Mouse over' - Area (A) = sclerosing adenosis; Area (B) = invasive carcinoma

Detail of above image - Area (A) = sclerosing adenosis; Area (B) = invasive carcinoma

Positive CK 5/6 staining of sclerosing adenosis area (A) and negative staining in invasive area (B)

Positive CK 5/6 staining of sclerosing adenosis area (A) and negative staining in invasive area (B)

Low grade invasive carcinomas v benign tubular pattern proliferations


In the following example the H&E appearances are strongly indicative of the diagnosis of Tubular Carcinoma. Immunostaining for myoepithelial markers shows an intact myoepithelial layer on the right hand side of the picture marking an intact duct with negative staining of the tubular (carcinoma) area.

As a practice point it is very reassuring to have a focus of positive staining in a section where the answer to the problem is being given by negative staining thus proving that the stain has worked and is not simply a technical failure (false negative).



Grade 1 invasive carcinoma - this is a tubular carcinoma to illustrate the difference from a radial scar
Low power - The tubules are more randomly scattered than in a radial scar and do not appear to be pinched in the middle
Medium power H&E of tubular carcinoma - there is no trace of a myoepithelial layer around these tubules CK 5/6 - Note absent myoepithelial layer around tumour acini and an entrapped normal/hyperplastic duct showing an intact layer

For a further example of use of immunohistochemistry in this diagnostic area click here:

Nipple adenoma


Nipple adenoma is a benign glandular proliferation presenting as a nodule beneath the nipple. On core biopsy its overall benign architecture can be difficult to appreciate and immunohistochemistry is very helpful in confirming the presence of an intact myoepithelial layer throughout the lesion.

In the example of an excised lesion below CK 5/6 shows rather weak and patchy staining however P63 is totally convincing.



Low power view of nipple adenoma
'Mouse over' for medium power image - a dual cell population can be appreciated at this power

Nipple adenoma - medium power view


CK 5/6 staining confirms the presence of an intact myoepithelial layer - it is weak in areas
'Mouse over' for P63 stain

Nipple adenoma - P63 stain highlights intact myoepithelial layer throughout


For further immuno images from this lesion click here:



For a further example of this entity click here:



Papillary lesions, ADH & DCIS


Differentiating intraduct papillomas from papillary carcinoma can be difficult. In addition to architectural and cytological characteristics of these two lesions (see also xxxx.html) benign papillary lesions are characterised by the retention of a myepithelial population often throughout the lesion. The following sequence of images illustrate this point.

In the papilloma images the immunostain 'P63' has been used - this stains nuclei of myoepithelial cells. In the papillary carcinoma ck 5/6 has been used which stains the cytoplasm of myoepithelial cells.



Intraduct papilloma
Low power view of benign papillary lesion High power view of benign papillary lesion showing dual population of epithelial and myoepithelial cells and well formed fibrovascxular cores
Dual population of epithelial and myoepithelial cells demonstrated clearly by CK 5/6 staining Dual population of epithelial and myoepithelial cells can also be demonstrated clearly by P63 staining - this is a nuclear stain



Papillary intraduct carcinoma
Fine papillary fronds with poorly formed fibro-vascular cores and composed of a single population of epithelial cells The presence of a single population of epithelial cells is underlined by complete absence of CK 5/6 staining



The following sequence of images demonstrates the use of CK 5/6 staining to confirm the presence of a mixture of luminal epithlial and myoepithelial cells in this severely atypical proliferation. In spite of the admixture of cell types the cytological atypia is so extreme this must be regarded as an example of high grade DCIS



Mixed intraductal proliferation of atypical luminal epithelial cells and myoepithelial cells
'Mouse-over' for CK 5/6 immunostain

Medium power view of duct - CK 5/6 staining confirms numerous myoepithelial cells admixed with atypical luminal epithelial cells


High power view of above duct with severely atypical intraductal proliferation - High grade DCIS

High power view of duct with moderately severely atypical intraductal proliferation



In DCIS the proliferating population of malignant cells is usually devoid of admixed myoepithelial cells giving a uniformly negative staining pattern in the duct but with a complete or partial peripheral rim of surrounding myoepithelial cells. This pattern is usually evident in DCIS of all grades.


DCIS - Low nuclear grade; cribriform pattern
Cribriform arrangement of epithelial cells of a single cell type expanding this duct CK 5/6 staining shows a peripheral rim of an intact myoepithelial layer but no staining whatsoever in the cell population expanding the duct - this is a pure population of luminal type epithelial cells


In situ v microinvasion



  • A microinvasive focus is by definition < 1mm
  • Microinvasion usually occurs in the context of extensive high grade DCIS
  • Clues to its presence are inflammation and fibrosis around the affected duct
  • The inflamed area should be searched for possible malignant cells either singly or in small groups
  • Pan CK or CK7 markers are good to help pick out small nests of cells outside the duct
  • Myoepithelial markers are helpful but their absence around a duct is not diagnostic of invasion/microinvasion
  • Microinvasive disease can metastasise


High grade DCIS with foci of microinvasion
Medium power H&E of a breast duct with high grade DCIS showing early disruption of its basement layers and surrounding fibrosis This CK 5/6 stain shows the same duct as on the left with a partially defective myoepithelial layer
DCIS - Periductal zone showing chronic inflammation and fibrosis and occasional single (microinvasive) tumour cells Single microinvasive tumour cells demonstrated very well with this cytokeratin stain
High power H&E of periductal inflammation with small groups of eosinophilic tumour cells within Numerous tumour cells highlighted with this CK 7 immunostain

See also Image of the week/month 2010/4 Use of CK5/6 immunohistochemistry in the diagnosis of DCIS v invasion.


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