Test Name: PAX-8

Methodology: IHC

Test Description

This protein is a member of the paired box (PAX) family of transcriptionfactors. Members of this gene family typically encode proteins which contain a paired box domain, an octapeptide, and a paired-type homeodomain. This nuclear protein is involved in thyroid follicular cell development and expression of thyroid-specific genes. Mutations in this gene have been associated with thyroid dysgenesis, thyroid follicular carcinomas, and atypical thyroid adenomas. PAX-8 is expressed in the thyroid (and associated carcinomas), non- ciliated mucosal cells of the fallopian tubes, and simple ovarian inclusion cysts, but not normal ovarian surface epithelial cells. PAX-8 is expressed in a high percentage of ovarian serous, endometrioid, and clear cell carcinomas, but only rarely in primary ovarian mucinous adenocarcinomas. Studies have also found PAX-8 expression in renal tubules as well as renal cell carcinoma, nephroblastoma, and seminoma. A study by Tong et al. showed that 98% of clear cell RCCs, 90% of papillary RCCs, and 95% of oncocytomas were positive for anti-PAX-8 with frequencies of positivity that are similar to anti-PAX-2. Therefore, anti-PAX-8 may be used as an additional immunohistochemical marker for renal epithelial tumors. Normal lung and lung carcinomas do not express PAX-8. Similarly, the absence of expression of PAX-8 in breast and other non-GYN carcinomas other than those primary to the thyroid indicates that anti-PAX-8 is an important new marker of ovarian cancer and a useful marker for the differential diagnoses in lung and neck tumors, or tumors at distant sites where primary lung carcinoma, breast carcinoma or thyroid carcinoma are possibilities. Anti-PAX-8, combined with organ system-specific markers such as anti-uroplakin III, anti- mammaglobin, and anti-TTF-1, can collectively serve as a very useful panel to determine the primary site of invasive micropapillary ovarian carcinomas from invasive carcinomas arising from bladder, lung, and breast.

Specimen Requirements

A formalin-fixed, paraffin-embedded (FFPE) tissue block is preferred specimen type or one (1) unbaked, unstained slide cut at 4-5 microns for H&E staining (required) and two to three (2-3) positively charged unstained slides cut at 3-4 microns for each test/antibody ordered.

Storage and Transport

Use cold pack during transport of paraffin blocks and unstained slides. Cold pack should not be placed in direct contact with the specimen during shipping

Specimen Rejection Criteria

Click here to reference the specimen rejection criteria.

Turn Around Time (TAT): 2-3 Days

CPT Codes*: 88341, 88342, 88360

*The CPT codes provided with our Test Descriptions are based on AMA guidelines and are for informational purposes only. Correct CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed.