Genetic and molecular genetic studies in the diagnosis of atypical lymphoid hyperplasias versus lymphoma.

The major emphasis in this section of the Workshop was the use of molecular diagnostic techniques in the differential diagnosis of benign versus malignant lymphoid proliferations at nodal and extranodal sites. In 1 case, these techniques were used to help make a very specific benign diagnosis. In the remaining cases, their main intention was to help prove that a lymphoid proliferation was benign or malignant. Review of the cases described herein highlighted both their utility in this regard as well as how they can be problematic and misleading. They also highlighted how important it is for the diagnostic pathologist to know the precise studies performed and to correlate the results with the morphological, phenotypical, and other findings before reaching a conclusion. Some of these issues are discussed in greater detail herein. J. Melnick, S. Shenoy, and M. Kraus of Washington University in St. Louis discussed a classic case (90) of autoimmune lymphoproliferative syndrome (ALPS) (or Canale-Smith syndrome).1 A 16-month-old male presented with anemia, adenopathy, and splenomegaly and a lymph node biopsy showed a very worrisome and very typical interfollicular lymphoid proliferation (Fig 1). Flow cytometric analysis of the “large cell” gate and immunohistochemical evaluation of the interfollicular cells demonstrated the following classic “double-negative” T-cell phenotype: CD2 , CD3 , CD5 , and CD43 with diminished CD7 but absent CD45RO, CD4, CD8, gamma-delta, CD20, CD30, CD56, myeloperoxidase, cytomegalovirus, and Epstein-Barr virus.1 Southern blot analysis did not demonstrate evidence of either a clonal B-cell or T-cell population. Fas (CD95) gene sequencing showed a heterozygous mutation in the death domain. These findings supported the benign nature of the lymph node biopsy and confirmed the diagnosis of ALPS. It is of interest that the patient’s mother is also heterozygous for the mutation so that, as is well recognized, other factors must play a role in the phenotypic expression of this disorder.2,3 The child was reported to be doing well at 6.5 years on low-dose steroid therapy. Criteria for ALPS include (1) chronic nonmalignant lymphoproliferation, (2) defective lymphocyte apoptosis in vitro and (3) 1% T-cell receptor (TCR) alpha/beta , CD4 , CD8 (double-negative) T cells in peripheral blood and/or the presence of doublenegative cells in lymphoid tissue.2 In addition to the marked paracortical expansion as described earlier, the lymphoproliferation includes florid follicular hyperplasia often with progressively transformed follicular centers and a polyclonal plasmacytosis.1 The double-negative T-cell population also expresses cytotoxic proteins, such as TIA-1, and many are CD57 .1 A CD5 polyclonal B-lymphocytosis is also characteristic.1 Supporting criteria include autoimmunity/autoantibodies and mutations in TNFRSF6 (Fas gene), FasL (Fas ligand), or caspase 10 gene. Fas is a cell surface receptor that binds Fas ligand and then initiates apoptosis initially by binding FADD, which in turn leads to activation of caspase 8 or 10. Patients with ALPS usually present as infants or young children with lymphadenopathy, splenomegaly, and variable autoimmune phenomena, particularly hemolytic anemia and thrombocytopenia. Hepatomegaly is seen in about 50% of patients. There are also many other less common clinical manifestations.2 Although the lymphoproliferative component is said to regress over time, the autoimmune phenomena are more likely to occur. Molecular studies have been used to identify 4 different types of ALPS.4,5 These include cases with generally heterozygous mutations in TNFRSF6 (type Ia), in the Fas ligand gene (Ib) or in the gene for the “downstream” caspase 10 (II), and those without any recognized molecular abnormalities (III). The Fas mutations are found throughout the gene, but most are in the exon that contains the death domain. Mutations in the extracellular portion of Fas are less likely to have ALPS and, if they do, to have less severe ALPS.4 It should be recognized that Fas gene mutations are not restricted to patients with ALPS and their relatives. Fas mutations occur normally in germinal centers,6 have been reported in a patient fulfilling the criteria for systemic lupus erythematosus,7 and occur in mucosaassociated lymphoid tissue and other lymphomas8 as well as in other malignancies.2 Molecular studies are also important in these cases, because they can be used (as in the case presented here) to support a benign diagnosis in the face of worrisome morphology by failing to demonstrate a From the Division of Hematopathology, University of Pittsburgh Health System, Pittsburgh, PA. Accepted for publication December 1, 2002. Address correspondence and reprint requests to Steven H. Swerdlow, MD, UPMC-Presbyterian, UPMC Health System, Division of Hematopathology, 200 Lothrop St., Room PUH C606, Pittsburgh, PA 15213-2582. © 2003 Elsevier Inc. All rights reserved. 0046-8177/03/3404-0008$30.00/0 doi:10.1053/hupa.2003.95