Clonal Evolution During Long-Term Follow-up Using Fluorescent in-Situ Hybridisation (FISH) in Chronic Lymphocytic Leukemia.
Authors: Norin Stefan , Aggarwal Mohit , Wallblom Ann , Kimby Eva 
Published: October 2019

Abstract
Abstract 4218

Background
The prognostic importance of certain chromosomal abnormalities in CLL is well-known. It is also established knowledge that deletions of the short arm of chromosome 17, del(17p), is more commonly found in chemoresistant patients. However, there is still uncertainty on how findings of small clones should be interpreted and only scarce sequential data of existing clones and emergence of new aberrations.

Aim
To evaluate the chromosomal aberrations del(13q), del(11q), del(17p) and trisomy 12 (+12) during the course of the disease with fluorescent in-situ hybridisation (FISH), with focus on the emergence of new clones and progression of existing clones.

Patients and methods
All patients from Karolinska University Hospital, Huddinge, diagnosed with CLL between 1983-2007 and with at least two FISH analyses on blood or bone marrow at different time points during the course of the disease were selected for further prospective samples (also from lymph nodes and spleen). In total 168 samples from 51 patients have been analysed (≥ 3 samples in 32 patients). Median age at diagnosis was 59 (range 35-77) years. The first FISH sample was taken at diagnosis in 25 patients, before any therapy in further 17 patients, and in the remaining 9 patients after therapy. Median time between the first and last FISH sample was 44 (range 4-300) months. Before the last FISH analysis totally 34 patients had been treated with purine analogs (n=13), alemtuzumab (n=5) and both these drugs (n=10). The remaining six patients were treated with alkylator-based therapy only.

Results
At the first FISH analysis, all but two patients had at least one aberration (96%) using a 5% cut-off; 23 with a single abnormality, del(13q) in 13 cases, del(17p) in 4 cases and +12 and del(11q) in 3 cases each. A combination of two or three aberrations was found in 26 patients. In total the most common aberration was del(13q) (n=32). Del (17p) was found in 24 patients and del(11q) and +12 in 18 and 7 patients, respectively.
Clones affecting more than 50% of the cells were mostly stable during follow-up, which was also the case for small clones (≤20% of the cells) with del (17p) in 17 out of 19 cases. However, a small del(13q) clone progressed in 3 out of 9 such cases.
New clones appeared during the course of the disease in 15 patients (29%); five new del(17p), two +12 and four cases each with del(13q) and (11q). All patients except four had been treated before the new clone emerged. New aberrations in these four untreated patients were del (17p) (n=2), del (13p) (n=1) and +12 (n=1). New clones did affect > 20% of the cells in only four cases; 2 del(13q) and 2 del(11q).

Sequential analyses of chromosomal aberrations with FISH during long-term follow-up of CLL patients show a low likelihood of progression of small del(17p) clones, but a clonal evolution in a third of patients including all the analysed aberrations. Further FISH analyses from spleen and lymph nodes will be presented at the ASH meeting.

Disclosures:
No relevant conflicts of interest to declare.