Cytogenetic Abnormalities In the Spleen In CLL Patients.

In CLL the prognostic importance of cytogenetic abnormalities in bone marrow or peripheral blood is well-known. However data is lacking on the frequency and importance of the aberrations in other tissues such as lymph nodes and spleens.

To develop a method to assess the chromosomal aberrations commonly seen in CLL (13q-, 11q-, 17p- and +12) on paraffin-embedded tissue sections from spleens and to relate the findings to data on abnormalities found in bone marrow or peripheral blood.

24 out of 61 CLL patients splenectomized between 1990–2009 have so far been analyzed. Paraffin-embedded sections were obtained from stored tissue material from spleen. Fluorescence in situ hybridization (FISH) was used to detect cytogenetic abnormalities and the results were compared with analyses made on blood or bone marrow. Monosomy 12, an abnormality rarely occurring in CLL was used as a surrogate marker to avoid false-positive results for deletions due to incomplete nuclei. In all but one case this was below 20%. Therefore the cut-off for the deletions (13q-, 11q- and 17p-) were set to 30%. For +12 we used 5%. Data on flow cytometry for quantification of the CLL clone in the spleen was available in 13 patients with a median of 71% clonal cells (range 11–86%). Indications for splenectomy were splenomegaly (n=13), AIHA (n=8) or ITP (n=3). All but five patients had received chemotherapy before splenectomy including purine analogs (n=7), alemtuzumab (n=1) or both (n=2) The remaining patients were treated with alkylators and/or anthracycline-containg regimens.

In all but one patient, FISH results from the splenic sections could be obtained with cytogenetic aberrations detected in 18 of 23 patients (78%). In 11 patients a single abnormality was detected, whereas multiple aberrations were present in 7 cases. The most common aberration was 13q- (70%), followed by 17p- (22%), 11q- and +12 (17% each) (Table 1). In 8 cases FISH samples from blood/bone marrow were available from time points both pre- and post- splenectomy and 6 additional cases had FISH data before splenectomy. All FISH abnormalities affecting >20% CLL cells in blood or bone marrow were also found in the spleen. In contrast an additional 17p clone was found in one patient and in two patients the 13q- and 17p- clones were significantly larger in the spleen. Remarkably one patient had both homo- and heterozygous 13q- clones in blood and in the spleen. In repeated blood samples nine years after splenectomy only a heterozygous clone remained.

FISH on paraffin-embedded sections is a useful tool for the evaluation of genetic abnormalities. Clonal evolution does appear to occur in the spleen in CLL and with splenectomy selected clones might be obliterated.

Kimby:Roche, Bayer-Schering, Mundipharma: Membership on an entity's Board of Directors or advisory committees, lecturer.