Comparative Immunohistochemical Analysis of Pulmonary and Thymic Neuroendocrine Carcinomas Using Pax8 and TTF-1
Annikka Weissferdt, Neda Kalhor, Cesar A Moran. University of Texas Health Science Center at Houston, Houston, TX; MD Anderson Cancer Center, Houston, TX
Background: Pax8 has recently been described to be expressed in thymic epithelial neoplasms and a subset of neuroendocrine carcinomas (NEC) of gastrointestinal origin but not pulmonary NEC. Thyroid transcription factor 1 (TTF-1) is known to be positive in NEC of pulmonary origin but studies investigating the expression of this marker in thymic NEC are lacking. To date, there are no comprehensive studies focusing on the comparative expression of Pax8 or TTF-1 in pulmonary and thymic NEC.
Design: Twenty-five cases of low and intermediate grade NEC of pulmonary and thymic origin, respectively were reviewed and representative sections were selected for immunohistochemical studies using antibodies directed against Pax8 and TTF-1. The percentage of positive tumor cells as well as the intensity of staining were evaluated and scored.
Results: Among the 25 pulmonary NEC were 21 low grade (typical carcinoid) and 4 intermediate grade (atypical carcinoid) tumors; the thymic tumors consisted of 8 low grade and 17 intermediate grade NEC. Only 2 (8%) of the pulmonary tumors showed nuclear expression of Pax8 whereas 19 (76%) expressed TTF-1. Of the thymic tumors, 8 (32%) were positive for Pax8 and only 2 (8%) showed TTF-1 positivity.
Conclusions: Primary NEC of the thymus are rare neoplasms that display a more aggressive clinical course than their pulmonary counterparts. Due to their rarity, metastasis from a pulmonary tumor always needs to be excluded by clinicoradiological means before a diagnosis of primary thymic tumor can be rendered. To date there are no specific immunomarkers to distinguish between neuroendocrine tumors of pulmonary and thymic origin. The differential expression of Pax8 and TTF-1 may prove useful in this context as a Pax8+/TTF-1- immunophenotype appears to be more common in thymic NEC while the reverse (Pax8-/TTF-1+) is true for pulmonary NEC.
Wednesday, March 6, 2013 1:00 PM
Poster Session VI # 287, Wednesday Afternoon