Significance of Conventional Cytogenetics in Improving the Diagnosis and Prognosis of Lymphoid Neoplasms in Tissue Samples
Authors: Meloni-Ehrig Aurelia , Curtis Christine A. , Mahoney Sean P. , Bohls Nathan , Kraemer Claudia , Stone Elizabeth , Braun Jean , Siragusa Kaye , Stone Patricia , Ramos Adrienne , Thompson Christopher , Daugherty Fred , Conklin Steve , An Caroline , Aftab Lalarukh , Hammami Amir , Schniederjan Stephanie , Lou Zhenjun , Dai Zunyan , Lyons Jill , Hertzberg Lawrence 
Published: October 2019

Abstract
Cytogenetic analysis is invaluable for the detection of chromosome abnormalities in tumor samples and is the "gold standard" technique (unique in providing a complete overview of the chromosome complement). Cytogenetic studies of lymph node specimens (LN) can be challenging due to progressively smaller biopsies being procured, low viability, and low proliferative rates. Typically, the initial laboratory evaluation of LN includes flow cytometry and/or immunohistochemistry. Due to overlapping immunophenotypic and morphologic features of some lymphomas, these studies can be insufficient to properly classify a lymphoid neoplasm. Interphase FISH is the test most frequently utilized for LN genetic evaluation. Although FISH has higher sensitivity than conventional cytogenetics, there is vast literature on the existence of cytogenetic abnormalities that are not targeted by the FISH probe(s) used in most laboratories. This is predominantly true for CLL/SLL, but it is also seen in other lymphomas, particularly those characterized by variant translocations involving closely related genes, such as mantle cell lymphoma with alternate translocations involving the CCND2 or CCND3 genes, or lymphomas carrying MYC rearrangements where the partner is not IGH (translocation partners other than Ig genes might merit less aggressive therapy). To achieve the same information obtained from an abnormal karyotype, it is usually necessary to perform multiple FISH tests with significantly increased costs. Genomic microarray and sequencing also have limitations. Microarray can only detect DNA unbalances (missing the balanced translocations that characterize most lymphomas). These whole genomic tests cannot detect multiple related clones indicative of clonal evolution, or unrelated clonal populations indicative of distinct lymphoid neoplasms in the same specimen. Successful cytogenetics offers the best visual representation of the whole chromosome complement and often yields information making it unnecessary to perform additional genetic tests. It should be noted that alternative genetic tests are extremely useful for cases with normal chromosome results or those that lack metaphase cells for analysis, as well as those with cytogenetically cryptic rearrangements or mutations. Recent studies indicate that complex karyotypes in lymphomas are, in general, indicative of transformation and/or worse prognosis. In the present study, for example, several follicular lymphoma cases displayed other abnormalities in addition to the typical t(14;18), some of which are known to be associated with transformation, i.e., deletions 1p, 6q, and 10q. We present our experience with 362 LN received over a 15 month period during 2014 and 2015. See Table below. Through correlation with all diagnostic test results from our laboratory, we demonstrate the unique value of cytogenetic evaluation of lymphoid tissues, optimizing diagnostic/prognostic assessment and, thereby, improving patient management/therapeutic decisions, while achieving cost reduction.
Table. A) Summary of cases and subdivision based on successful cytogenetics and normal or abnormal flow/morphology versus normal or abnormal cytogenetics; B) Detailed information on the number of the various lymphoid neoplasms included in our study. Total Cases: 362 No metaphases: 67 (19%) With metaphases: 295 (81%) Normal flow/morphology and normal cytogenetics 74 (25%) Abnormal flow and/or morphology 221 (75%) Normal cytogenetics: 59 (27%) Abnormal Cytogenetics: 162 (73%)
Table. Final Diagnosis (Abnormal cytogenetic cases) # cases Sex (M/F) # FISH FISH Abnormal/normal FL 56 25/31 43 43/0 SLL/CLL 32 20/12 21 20/1 HGL 14 7/7 0 0 TCL 14 7/7 5 3/2 MZBCL 13 8/5 8 5/3 DH/THL 10 6/4 10 10/0 DLBCL 8 4/4 8 7/1 MCL 7 4/3 5 4/1 CD30+ 2 0/2 2 1/1 NGCL 2 0/2 2 1/1 BL 1 1/0 1 1/0 LPL 1 1/0 0 0 B-ALL/LBL 1 0/1 1 1/0 HL 1 1/0 1 1/0 Totals 162 84/78 107 (66%) 97/10 Abbreviations: FL, follicular lymphoma; SLL/CLL, small lymphocytic lymphoma/chronic lymphocytic leukemia; HGL, high-grade lymphoma; TCL, T-cell lymphoma; MZBCL, marginal zone B-cell lymphoma; DH/THL, double hit/triple-hit lymphoma; DLBCL, diffuse large B-cell lymphoma; MCL, mantle cell lymphoma,; CD30+, CD30-positive large B-cell lymphoma; NGCL, non-germinal center lymphoma; BL, Burkitt lymphoma; LPL, lymphoplasmacytic lymphoma; B-ALL/LBL, B-cell acute lymphoblastic leukemia/lymphoblastic lymphoma; HL, Hodgkin lymphoma.

Disclosures
No relevant conflicts of interest to declare.