Immunohistochemistry

Cytokeratins are intermediate filaments present in all epithelial cells, and also in a number of non-epithelial cells. In fact, cytokeratin positively has been reported in almost every tumour type, including uterine smooth muscle tumours, most soft tissue sarcomas, melanomas, gliomas, plasmacytomas and occasionally lymphomas.

Cytokeratins can be differentiated into light and heavy chain based on their molecular weight as well as acidic which are cytokeratins 9-20 or basic which are cytokeratins 1-8.

Diagnostic utility

Identification of carcinomas

Identification of sarcomas showing true epithelial differentiation like synovial sarcoma or epithelioid sarcoma

CK 8 is a keratin protein found in humans. This has several uses but as can be seen in Ck5.2, it is most useful when combined with Ck 18.

Picture 1 – CK 8 positivity in Adenocarcinoma

Ck 8 has several different applications. Below are a few examples.

Tumour	CK 8 + or -
Epitheliod sarcoma	Positive
GIST or Gastrointestinal Tumour	Positive
Angiosarcoma	Positive in 85% of cases, but has specificity issues
Karposi Sarcoma	Variable positive in about 85% of cases, but has specificity issues
Synovial Sarcoma	Negative

CK 18 is found in most simple ductal and gladular epithelia. A cytoplasmic staining is produced as shown below in the colon but also skin can be used as a control in diagnostic settings. Again this is most useful when combined with CK8.

Picture 2 – CK 18 positivity in colon

CK 18 has several different applications. Below are a few examples.

Tumour	CK 18 + or -
Epitheliod sarcoma	Positive
GIST or Gastrointestinal Tumour	Positive
Angiosarcoma	Positive in 85% of cases, but has specificity issues
Karposi Sarcoma	Variable positive in about 85% of cases, but has specificity issues
Synovial Sarcoma	Negative

CK 19 reacts with a range of epithelial malignancies. These inclue as shown below adenocarcinomas of colon, stomach, pancreas, liver and breast. A cytoplasmic staining is produced as shown below in the colon but also skin can be used as a control in diagnostic settings.

Picture 3 – CK 19 positivity in Adenocarcinoma

CK 19 has several different applications. Below are a few of the most common examples.

Tumour	CK 19 + or -
Papillary Thyroid Carcinoma	Positive
Thyroid Follicular Carcinoma	Positive - around 50/60% of the time
Pancreas Ductal Carcinoma	Positive
Neuroendocrine Tumour	Variable positive in about 50% of cases
Pancreatoblastoma	Negative

CK 5.2 has several different applications. It produces a cytoplasmic staining which is very useful in distinguishing adnemocarcinoma and non-keratinizng squamous cell carcinoma from kertainizing squamous cell carcinoma.

Picture 4 – CK 5.2 positivity in Adenocarcinoma

As can be seen below CK 5.2 has several different applications. Below are a few examples.

Tumour	CK 5.2 + or -
Peripheral nerve sheath	Positive
Spindle squamous cell carinoma	Positive
Kaposiform Hemangioendothelioma	Positive
Keratinizing squamous cell carcinoma	Negative
Karposi Sarcoma	Negative

Immunohistochemistry- Light molecular weight CKs

Diagnostic utility