Eradication and Reduction of the Abnormal Chromosome 7 Clone with Azacitidine (AZA C) Is Achievable for One-Third of Patients (pts) with Myelodysplastic Syndrome (MDS).

The two most frequent cytogenetic abnormalities in pts with MDS involve rearrangements of chromosomes 5 and 7. Monosomy 7 or deletion 7q, alone or in a complex karyotypes are poor-risk abnormalities and associated with a low response rate to conventional therapies. As a part of our comprehensive longitudinal study of 220 patients treated with AZA C, we asked the question whether pts with −7/del(7q) alone or as a part of the complex clone, may achieve hematological and/or cytogenetic response. A minimum of three follow-up cytogenetic and FISH analyses were required as an inclusion criterion. A normal karyotype was observed in 129 of 229 pts (56%) and 100 pts (44%) had an abnormal karyotype at baseline. Among the 100 pts with an abnormal karyotype 29 pts (29%) had chromosome 7 abnormalities prior to the AZA C treatment. In an additional 12 pts chromosome 7 abnormalities developed during the course of disease and AZA C therapy (range 4 months to 5 years). Response of the abnormal chromosome 7 clone to AZA C therapy was observed in 3 patterns:

1. pts who had −7/del(7q) present at baseline without any further cytogenetic change during the AZA C treatment (20 pts; 69%). Eight of these pts had hematological improvement (HI);

2. Pts who had either reduction or elimination (complete cytogenetic response=CCR) of the abnormal chromosome 7 clone as a results of treatment (9 pts, 31%).

Four of 29 pts (14%) had a reduction in the size of the abnormal clone from 100% to a mean of 23% (range 8%–50%) as judged by conventional cytogenetics. The median time to achieve reduction was 6 months (range 2 to 9 months) with median duration of 10.5 months (range 6 to 24 months) during maintenance therapy with AZA C. CCR was observed in 5 of 29 pts (17%) and occurred within a mean of 4.2 months (range 3–6 months). Repeated cytogenetic studies showed a normal karyotype and the CCR lasted a mean of 5.2 months (range 3–9 months) during therapy. FISH studies showed 2–5% cells with −7/del(7q) during the CCR. Four of the 5 pts had HI and one pt had CR. These patients relapsed with the diagnostic −7/del(7q) clone without additional cytogenetic abnormalities. 3) Of the 12 pts who developed −7/del(7q) while on Aza C therapy, 4 pts had a normal karyotype at baseline and developed −7/del(7q) after a mean of 16 months (range 6–39 months) therapy. One had PR and 3 pts had a stable disease. The other 8 pts were cytogenetically abnormal at baseline and developed −7/del(7q) as a subclonal evolution during therapy in 4 pts (range 4 months to 5 years) and following disease progression in 4 pts. Six pts had HI and two had a stable disease. In conclusion, our longitudinal study allowed us to delineate 3 categories of AZA C response to abnormal chromosome 7 clone:

1. 31% had cytogenetic response: 17% complete and 14% major and

2. 69% had no change in the abnormal −7/del(7q) clone.

In additional 5% (12/229) pts, −7/del(7q) emerged either as a new abnormal clone or as a subclonal evolution during therapy or at progression. AZA C-based therapy can either stabilize or reduce/eradicate the abnormal chromosome 7 clone as determined by both, cytogenetics and FISH.