What is the differential diagnosis for a liver biopsy showing CK7 (Cytokeratin 7) negative and CK20 (Cytokeratin 20) negative staining?

Differential Diagnosis for CK7-Negative/CK20-Negative Liver Biopsy

A CK7-negative/CK20-negative adenocarcinoma on liver biopsy requires immediate expanded immunohistochemical workup to identify the primary site, as this atypical phenotype has poor predictive value and represents an unexpected pattern that cannot reliably guide clinical investigation without additional markers. 1

Primary Diagnostic Considerations

The CK7-/CK20- phenotype is diagnostically challenging and represents the least informative cytokeratin pattern for liver metastases. The differential diagnosis includes:

Most Likely Primaries

• Hepatocellular carcinoma (HCC) - This is the most critical diagnosis to exclude, particularly in patients with chronic liver disease or cirrhosis. HCC can present with a CK7-/CK20- pattern and requires hepatocellular markers (HepPar-1, glypican-3, Arginase-1, alpha-fetoprotein) and/or canalicular markers (CEA, CD10, BSEP) for confirmation. 1

• Metastatic colorectal carcinoma - While the classic colorectal phenotype is CK7-/CK20+, approximately 5% of colorectal metastases can be CK20-negative. This represents an unusual but possible profile. 1

• Renal cell carcinoma metastases - These characteristically show CK7-/CK20- pattern and should be evaluated with renal markers. 2

• Prostate adenocarcinoma (in males) - Must be excluded using PSMA and/or NKX3.1 markers. 1

• Breast carcinoma (in females) - Particularly triple-negative breast cancer, which requires GATA3 and/or SOX10 staining for evaluation. 1

Less Common Considerations

• Intrahepatic cholangiocarcinoma (iCCA) - While the typical phenotype is CK7+/CK20-, unusual profiles occur in <5% of cases where CK7 can be negative. C-reactive protein (CRP) immunostaining is highly sensitive (97%) for small-duct subtype iCCA and should be added to the panel. 1

• Neuroendocrine tumors - These may show minimal or absent cytokeratin expression and require synaptophysin and/or INSM1 staining for identification. 1

• Sarcoma or melanoma - Consider if broad-spectrum keratin staining is only focal, requiring SOX10 and/or S100 for melanoma evaluation. 1

Recommended Immunohistochemical Algorithm

Immediate next steps based on 2024 French Association for the Study of the Liver guidelines: 1

First-Line Panel (Priority Markers)

• CDX2 or SATB2 - To evaluate for intestinal/gastric origin (colorectal primary)
• TTF1 - To exclude pulmonary origin
• GATA3 (in women) - To exclude breast origin
• CRP (C-reactive protein) - To support cholangiocarcinoma diagnosis (76-93% sensitivity, 88-91% specificity)
• HepPar-1, glypican-3, Arginase-1 - To exclude hepatocellular carcinoma

Second-Line Panel (Based on Clinical Context)

• PSMA and/or NKX3.1 (in men) - To exclude prostate carcinoma
• Synaptophysin and/or INSM1 - If neuroendocrine morphology suspected
• SOX10 and/or S100 - If melanoma considered
• Renal markers - If clinical suspicion for renal primary

Critical Additional Step

• Biopsy of non-tumoral liver tissue is essential, as the presence of advanced fibrosis or cirrhosis dramatically shifts the differential diagnosis toward primary liver malignancies (HCC or scirrhous HCC variants). 1

Clinical Pitfalls and Caveats

• The CK20-/CK7- phenotype showed disappointing results in predicting primary tumor origin, with 60% of cases having unexpected primary localization and 37% remaining unknown even after full workup. 3

• Rare HCC variants can be CK20-positive (reported in <5% of cases), particularly in pseudoglandular patterns, which can confuse the diagnosis. Do not rely on CK20 alone to exclude HCC. 4

• Scirrhous HCC is often CK7+ and/or CK19+, making differentiation from cholangiocarcinoma difficult on biopsy alone. 1

• Immunohistochemical loss of BAP1 or ARID1A can support cholangiocarcinoma diagnosis but requires correlation with clinical and radiological findings. 1

Mandatory Clinical Correlation

• Multiphase CT of chest, abdomen, and pelvis is required to search for extrahepatic primary sites. 1

• Upper gastrointestinal endoscopy should be discussed in multidisciplinary tumor board to eliminate gastric cancer. 1

• FDG-PET scan may be considered if doubt persists regarding liver metastases versus primary tumor, to identify occult extrahepatic primary. 1

• Molecular profiling should be considered once tissue of origin is established for treatment planning. 5