Duplication of the long arm of chromosome 1 (1q) is widely reported in human 
neoplasia, including the myelodysplastic syndromes (MDS). So far, it has not 
been described as a single aberration in the chronic myelomonocytic leukemia 
(CMML), a subtype of MDS. Rather, trisomy 1q was always a part of complex 
chromosome changes affecting the subtypes of MDS other than CMML. We report on a 
patient with CMML with an unbalanced translocation of the entire 1q onto the 
short arm of chromosome 14 as a sole cytogenetic abnormality. Fluorescence in 
situ hybridization (FISH) analysis with an alpha-satellite probe for the 
paracentric region of the long arm of chromosome 1 confirmed the presence of 
trisomy 1q in a derivative chromosome, der(14)t(1;14)(q12;p11). The discrepant 
results between the metaphase cytogenetics (100% abnormal) and interphase 
cytogenetic (71% nuclei with 3 signals) suggest that trisomy 1q, even in the 
absence of additional cytogenetic changes, has a sufficient leukemogenic 
potential to confer a proliferative advantage on hematopoietic cells committed 
to monocyte stemline both in vitro and in vivo. The literature data on partial 
and complete trisomy 1q in CMML is reviewed.