Diagnostic impact of molecular lineage analysis on paraffin-embedded tissue in hematolymphoid neoplasia reclassified by current WHO criteria.
OBJECTIVE
By current WHO criteria, most - though not all - cases of hematolymphoid neoplasm can be diagnosed immunomorphologically, diminishing the role of molecular tests for lymphoid antigen receptor clonality in lymphoma diagnosis. Hence, our objective was to glean immunomorphological and molecular correlates from hematolymphoid neoplasms that had remained unresolvable without diagnostic molecular input.


METHODS
Thirty-five such cases were reviewed histologically and with standard immunoperoxidases. In situ hybridization for Epstein-Barr virus (EBV)-encoded RNAs (EBER) was performed on selected cases. PCR amplification of genes encoding T-cell receptors (TcR) and immunoglobulin heavy chains (IgH) [TR and IGH genes, respectively] was performed on whole tissue in all cases, and on microdissected cells in two cases.


RESULTS
Twenty-five cases (71%) requiring diagnostic molecular genotyping had some form of peripheral T-cell lymphoma (PTCL). Twenty (80%) of these were complicated by a proliferation of B-lineage cells, either within the same tissue ('syntopic') as large B cells (LBC) or Reed-Sternberg (RS)-like cells (17 cases), florid lymphoid hyperplasia (two cases, one also with syntopic LBC) or monotypic plasma cells (one case), or at a separate ('metatopic') site as a B-cell lymphoma (two cases, one of which also had syntopic LBC) or Hodgkin lymphoma (HL; one case, also showing syntopic LBC). Fifteen (75%) of these 20 PTCLs with B-lineage proliferation yielded monoclonal TR gene rearrangements, and only two (10%) showed IGH monoclonality, which was transient in one case. Three (18%) of the PTCLs with LBC had originally been misinterpreted as some form of HL. Conversely, of the remaining cases, three of four (75%) that had been diagnosed initially as some form of large cell non-HL (NHL), including two of three that were called 'anaplastic', had to be revised to grade II/syncytial nodular sclerosing (NS) HL, yielding polyclonal TcRgamma gene (TRG) rearrangements, with one case, in addition, disclosing a biallelic clonal IGH gene rearrangement that excluded anaplastic large cell lymphoma.


CONCLUSIONS
Paradoxically, monoclonality of TR rather than IGH gene rearrangement may more often be detectable in a predominantly dispersed ('hodgkinoid'), large B-lineage cell proliferation, consistent with release from immune regulation in the milieu of impaired immunosurveillance within a PTCL. This is compounded by the difficulty in ascertaining clonal IGH gene rearrangements resulting from (1) poor consensus primer hybridization due to somatic hypermutations, and (2) 'dilution' in a T-cell-rich milieu. These same difficulties also account for the long-elusive identification of the RS cell lineage. Conversely, anaplastic lymphoma, which is of non-B lineage, may be mimicked by NSHL, which is of B lineage.
Tan
Leonard Hwan Cheong
LH
Department of Pathology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.leonard.tan.h.c@sgh.com.sg
Chiu
Lily-Lily
LL
Koay
Evelyn Siew Chuan
ES
D015703:Antigens, CD / Q000235:genetics; D001706:Biopsy; D005784:Gene Amplification; D015321:Gene Rearrangement; D005838:Genotype; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D017403:In Situ Hybridization; D016399:Lymphoma, T-Cell / Q000145:classification* / Q000235:genetics* / Q000276:immunology / Q000473:pathology; D016133:Polymerase Chain Reaction; D011948:Receptors, Antigen, T-Cell / Q000235:genetics; D014944:World Health Organization
D015703:Antigens, CD; D007143:Immunoglobulin Heavy Chains; D011948:Receptors, Antigen, T-Cell