FISH- Target Gene Panel Profile for Chronic Lymphocytic Leukemia/Small Cell Lymphocytic Lymphoma [CLL/SLL].
Authors: Reddy Kavita S. 
Published: October 2019

CLL/SLL test data for target FISH 4 probe (Vysis Inc) panel comprising of D13S319 (13q14.3)/LSI 13q34, LSI p53 (17p13.1), LSI ATM (11q22.3) to detect deletions (del) and CEP 12 to detect trisomy on the majority of cases and a 3 probe panel: MYB LSI 6q22–23 (homebrew), LSI ATM (11q22.3), and CEP 12 on 59 cases, along with flow cytometry, and cytogenetics were retrospectively analyzed.

A total of 888 CLL/SLL FISH tests were ordered, 509 [Av age 67.7yrs, <50 yrs = 36; M:F ratio 319:190; Specimen type: 239 Blood, 252 Bone marrow, 18 tissue] had CLL/SLL immunophenotype [light chain restricted B-cells coexpressing CD5 and CD19 with CD23], 59 had a differential diagnosis based on surface markers, 137 were polyclonal, normal immunophenotype or too few B-cells etc. and 124 had only a FISH test.

Among CLL/SLL flow confirmed cases 349 [349/509=68.6%] were abnormal for 4- probe panel FISH: 160 del 13q34 [45.8 % (122-del 13, 17-biallelic del 13, 21-mono/biallelic del)], 71 extra copy of 12 [20.3%], 17 del ATM [5%], 12 del p53 [3.4%], and 89 with ≥2 FISH abnormalities [25.5%]. Concurrent cytogenetic results obtained in 151 cases were abnormal in 43 [28.5%]. The FISH results in 108 normal karyotype cases were: 39 normal, 1 del ATM [in 20% cells], 4 del p53 [11–29%], 14 extra copy of 12 [14–79%], 35 del 13q34 [13–98%], 15 ≥ 2 FISH abnormalities. FISH results in 43 abnormal karyotype cases: a normal FISH result in 10 [1- balanced translocation, 3- loss of Y, 2-del 6q, 1-complex karyotype with del 6q, one t(8;14), 1-trisomy 8, and 1-t(13;15)(q14;q26)]. An extra copy of 12 by FISH had concordant +12 karyotype in 2 cases, loss of Y in 3, trisomy 15 in one, 2 had multiple changes with +12, 1 had multiple changes without +12. In 8 del 13q34 FISH cases, karyotypes showed a loss of Y in 4, concordant del 13q in one, multiple abnormalities not involving 13 in 2 cases of CLL with increased myeloblasts [9–10%] by flow were del 5q, del 7q and del 20q in one and deletions of 5q, 9q and 18q in the other. A del p53 FISH case showed a loss of 17 in a 3n+ karyotype. Of 15 cases with ≥ 2 FISH abnormalities, the karyotypes had partial concordance in 8, discordant in 6 and concordant in 1.

One of 59 [1.6%] tested with 3-probe panel had a del MYB [6q22–23] and 6 [6/151=4%] flow confirmed CLL with normal or multiple probe abnormalities for 4-probe panel had a cytogenetic del 6q. Of 10 cases considered as T-CLD 4 had ATM deletion and 6 were normal by FISH. In 14 CD23 negative cases IgH/BCL1 FISH probe detected t(11;14) and confirmed mantle cell lymphoma. Three cases were diagnosed with PLL, one had a deletion of p53 and an abnormal karyotype, two were normal by FISH. Multiple probes [Vysis Inc]/panels which included the IgH probe were ordered in 57 cases with CLL immunophenoype, 10 cases had an uncommon IgH rearrangement not included in the panels.

Because of the greater efficacy of FISH compared to karyotyping which is limited by difficulties in culturing lymphoid versus myeloid cells, chromosome analysis can be considered in conjunction with FISH for CLL. Although the 4-FISH probe panel stratified CLL by prognosis in 68.6 % cases, the addition of del 6q probe would enhance identifying cases with poor prognosis. Since IgH rearrangements appear to be prevalent, a 3 color IgH/BCL1 probe would increase the strength of the CLL panel by identifying any IgH rearrangement [usually associated with a more aggressive disease] and also provide a differential diagnosis, particularly, in CD23 negative cases.