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PAX8+ tumors

Wednesday 11 September 2019

PAX8-expressing tumors

Definition; PAX8 is a paired-box gene important in embryogenesis of the thyroid, Müllerian tract, and renal/upper urinary tracts. PAX8 is a highly sensitive marker for thyroid tumors, renal tumors, Müllerian tumors, and thymic tumors. Importantly, all lung adenocarcinomas, breast and adrenal neoplasms, and the majority of gastrointestinal tumors are negative for PAX8.

- PAX8 expression in thyroid tumors

  • thyroid SCC / thyroid squamous cell carcinoma
  • PAX8 is an excellent marker for confirming primary thyroid tumor in metastasis
  • In a subset of cases, additional markers, including but not limited to thyroid transcription factor-1 (TTF1), RCC, and Wilms tumor-1 (WT1), may be needed to distinguish between the 3 most common PAX8-positive tumors.
  • PAX-8 is key if differential is lung adenocarcinoma vs. thyroid carcinoma.
  • Pax8 is expressed in 79% of thyroid anaplastic carcinomas to a variable extent, whereas TTF-1 and TTF-2 were seen only in 18 and 7% of anaplastic carcinomas, respectively. (18084247)

- PAX8 expression in parathyroid tumors

- PAX8 expression in well-differentiated pancreatic endocrine tumors (PETs) (20414099)

  • PAXs (paired box) genes encode a family of transcription factors that regulate organogenesis and cell-lineage specification in multiple organ systems.
  • In the pancreas, PAXs proteins play a critical role in islet cell differentiation. We recently observed that islet cells show strong, diffuse staining for PAX8 by immunohistochemistry.
  • PAX8 is expressed in normal pancreatic islet cells and in a high proportion of primary and metastatic PETs.
  • In the GI tract, PAX8 is positive in the majority of duodenal and rectal carcinoid tumors, and in a minor subset of appendiceal and gastric carcinoids.
  • PAX8 expression is absent in ileal and pulmonary carcinoid tumors.
  • PAX8 immunostaining may be helpful in determining the primary site for a WDNET metastatic to the liver, as ileal (PAX8 negative) and pancreatic (PAX8 positive) tumors most often present as a metastasis from an occult primary.
  • PAX8 may also be a prognostic marker in PETs, as loss of expression is associated with malignant behavior.

- thymic tumors

  • Positive immunoreactivity for PAX8 is noted in 77% of thymic carcinomas, 100% of WHO type A thymomas, and 93% of WHO type B thymomas. (21836478)
  • Consistent but weaker staining for Pax8 is also identified in the epithelial cells of remnant thymic tissue located in the periphery of the tumors. (21836478)

- extraovarian primary peritoneal carcinoma (EOPPC)

- ovary tumors
- endometrial tumors
- endocervical tumors

- Merkel cell carcinoma
- nephrogenic adenoma