Patterns of PAX 8 Expression in Lymphomas
Shahid J Bokhari, Alok Mohanty, Jan F Silverman. Allegheny General Hospital, Pittsburgh, PA
Background: The PAX 8 gene, a member of the paired box (PAX) family of genes, encodes a transcription factor that plays a critical role in embryologic development of the thyroid, renal, and Müllerian systems. Expression of PAX 8 by immunohistochemistry (IHC) has been described in thyroid, renal, and Müllerian derived neoplasms. Recently, PAX 8 expression has been reported in lymphoma and non-neoplastic lymphoid tissues; however, there are no reports detailing the phenotypic expression and patterns of PAX 8 positivity in the subtypes of non-Hodgkin lymphoma (NHL), classical Hodgkin lymphoma (CHL), and non-neoplastic lymphoid tissues. Our study focuses on expression and patterns of PAX 8 positivity in different lymphoma subtypes that can potentially aid in classification.
Design: A total of 91 cases of NHL and 22 cases of CHL with H&E slides and corresponding tissue blocks were retrieved from the hospital computer system following IRB approval. All selected cases had been previously confirmed as NHL and CHL by histologic and IHC examination. IHC for PAX 8 was performed on all cases on tissue-block sections that were formalin-fixed and paraffin embedded, using a heat-induced epitope retrieval technique.
Results: 91 cases of NHL were included in our study: 25 diffuse large B-cell lymphoma (DLBCL), 20 follicular lymphoma (FL), 20 marginal zone lymphoma (MZL), 16 small lymphocytic lymphoma (SLL), 10 mantle cell lymphoma (MCL). 22 cases of CHL were also included in our study: 14 nodular sclerosing (NS), and 8 mixed cellularity (MC). In all cases, PAX 8 expression was seen in background non-neoplastic B-cells, but not in the T-cells, histiocytes, or plasma cells. PAX 8 demonstrated strong diffuse nuclear expression in the neoplastic cells in all cases of DLBCL, MZL, FL, MCL, and SLL. In all cases of FL and MCL, PAX 8 showed strong nuclear expression in both a follicular/nodular and diffuse pattern, mirroring the histologic pattern, respectively. In all cases of SLL, PAX 8 showed strong, diffuse, nuclear expression in the majority of the neoplastic cells with paler staining para-immunoblastic cells comprising the proliferation centers. All CHLs demonstrated PAX 8 expression in the neoplastic Reed-Sternberg cells while the background T-cells showed no expression of PAX 8.
Conclusions: 1) PAX 8 is a very good IHC marker for non-neoplastic and neoplastic B-cells and is consistently seen in a variety of subtypes of NHL.
2) PAX 8 stains the neoplastic cells in CHL, further supporting the B-cell origin of Reed-Sternberg cells.
3) The expression and pattern of PAX 8 positivity can be helpful in the work-up of a variety of NHL subtypes and CHLs.
Tuesday, March 20, 2012 1:00 PM
Poster Session IV # 212, Tuesday Afternoon