All IHC stains will include a positive control tissue

• CK 19 is useful in distinguishing papillary carcinoma (including follicular variant papillary carcinoma) from follicular adenoma, follicular carcinoma, and benign hyperplastic nodules
• CK 19 usually stains papillary carcinomas in a strong, diffuse pattern
• Normal thyroid parenchyma immediately adjacent to papillary carcinoma may also show strong to moderate reactivity
• Normal thyroid farther from papillary carcinomas will show no reactivity or rarely focal, weak staining
• One study³ reports CK 19 staining in follicular adenomas; in this study, 75% of follicular adenomas showed only scattered positive cells (usually confined to flattened cells lining cystic follicles)
• Focal CK 19 staining has also been reported in areas of degeneration, usually at the site a previous FNA
• Always correlate the immunohistochemical staining pattern with the histologic assessment including nuclear features
• CK 19 also stains biliary epithelium including biliary carcinomas
• CK19 is often co-expressed with CK7, and positive staining is often seen in lung carcinomas

Submit a formalin-fixed, paraffin-embedded tissue

Formalin-fixed, paraffin-embedded (FFPE) tissue block

FFPE tissue section mounted on a charged, unstained slide

Ambient (preferred)

• Unlabeled/mislabeled block
• Insufficient tissue
• Slides broken beyond repair

Immunohistochemical staining and microscopic examination

If requested, an interpretive report will be provided

Specifications

• CK 19 is a low-molecular-weight keratin present in simple epithelial cells
• CK 19 has been found to be present in papillary thyroid carcinoma, including follicular variants of papillary carcinoma
• It is absent or only rarely focally present in normal thyroid

Staining pattern

• Cytoplasmic

References

1. Zubair WB et al: Differential expression of cytokeratins in follicular variant to papillary carcinoma: an immunohistochemical study and its diagnostic utility. Hum Pathol 30:1166-1171, 1999.
2. Cheung CC et al: Immunohistochemical diagnosis of papillary thyroid carcinoma. Mod Pathol 2001;14(4):338-342.
3. Sahoo S et al: Cytokeratin 19 immunoreactivity in the diagnosis of papillary thyroid carcinoma; a note of caution. Am J Clin Pathol 2001;116:696-702.