Peripheral Blood Karyotyping Is Superior To Bone Marrow and Identifies Most Frequent Structural Chromosomal Rearrangements In Myelofibrosis

In the past cytogenetic studies of patients with MF were hindered because marrow (BM) specimens were used for karyotyping but frequently could not be obtained due to advanced marrow fibrosis. Since MF is characterized by the constitutive mobilization of immature myeloid cells into the peripheral blood (PB), we compared unstimulated PB specimens with BM specimens to determine their utility in successfully detecting cytogenetic abnormalities in patients with MF. We also simultaneously performed interphase FISH (IFISH) studies in order to determine if IFISH identified additional genomic abnormalities in MF. We evaluated 183 patients who had had successful conventional and molecular cytogenetic analyses. Our myeloproliferative neoplasm ( MPN)-FISH panel consisted of twelve probes (EGR1 at 5q31, D5S23 at 5p15.3, D7Z1 at 7p11-q11, D7S522 at 7q31, D8Z2 at 8p11-q11, CDKN2A at 9p21, CEP9 at 9p11-q11, ATM at 11q22,1, Rb1 at 13q14, and D20S18 at 20q12, CKS1B at 1q21 and CDKN2C at 1p32). BM cytogenetics was studied in 60 pts (33%) and PB cytogenetics were evaluated in 123 pts (67%). Conventional cytogenetics was informative for 96% (123/128) of PB specimens and 97% (60/62) of BM samples. When conventional cytogenetic analysis was compared to IFISH, concordant results were observed in 154 patients (84%). Moreover, conventional karyotyping identified chromosomal abnormalities in an additional 18 patients (10%), which were not targeted by the 12 loci FISH panel. Among these patients, structural abnormalities of chromosome 12 were detected in 6 patients (33%) which represents the most frequent structural abnormality detected in MF and was associated with poor survival. Of the 63 patients with concordant abnormal cytogenetics and FISH the most frequent abnormalities included: del(20)(q11q13) (n=30, 48%), unbalanced 1q translocations resulting in trisomy 1q or duplication of 1q (n=17, 27%), gain of chromosome 8 (n=9, 14%), +8,+9( n=4, 6%), trisomy 9 (n=4, 6%), del(7q)/-7( n=7,11%), deletion 13q (n=9,14%) and complex karyotype (n=16, 25%). The remaining 11pts (6%) had discordant conventional and molecular cytogenetic results and were divided into two categories: A) those with normal cytogenetics (with or without non clonal abnormalities) and an abnormal MPN IFISH panel and B) those with abnormal clonal karyotype with normal lFISH. When compared to BM, PB specimens had a similar rate of abnormal karyotype: 51% in PB vs 48% in BM. Our results unequivocally demonstrated that conventional cytogenetics of MF can be successfully obtained from unstimulated PB specimens in 96% of patients and that analysis of BM does not reveal additional cytogenetic abnormalities. We conclude that FISH analysis has limited value in MF and is only informative for those patients who lack mitotic cells or who are cytogenetically normal, and in these patients, IFISH detects cryptic abnormalities in 4%. Use of PB karyotyping in MF is sufficient to effectively detects clonal hematopoiesis which contributes to prognostic risk stratification and influences therapeutic decision making.