Table I.

Chromosome abnormalities (e.g., double-stranded chromosome breaks, chromatid breaks, fusion events) in controls and subjects with or without prior hydroxycarbamide exposure. Results represent mean number of events per 100 cells examined in metaphase chromosome spreads ± standard deviation. Final column represents p value obtained comparing subjects with and without prior hydroxycarbamide exposure using the Mann-Whitney U test. HC, hydroxycarbamide; XRT, external beam radiation

	Control	No HC Exposure	HC Exposure	p-value
Patients (n)	11	28	51
Age at Sample (years)	44.3 ± 11.0	9.4 ± 4.7	13.2 ± 4.3
0 Gy XRT/0 HC
Chromosome Breaks	0.1 ± 0.4	0.6 ± 0.8	0.3 ± 0.7	0.18
Chromatid Breaks	0.5 ± 0.5	1.0 ± 1.2	0.4 ± 0.8	0.04
Fusion Events	0.0 ± 0.0	0.3 ± 0.6	0.1 ± 0.3	0.52
Total Abnormalities	0.6 ± 0.7	1.9 ± 1.5	0.8 ± 1.2	<0.01
2Gy XRT/0 HC
Chromosome Breaks	19.7 ± 11.4	17.1 ± 7.0	21.4 ± 13.1	0.32
Chromatid Breaks	6.4 ± 4.7	6.8 ± 5.0	5.1 ± 4.2	0.07
Fusion Events	4.6 ± 2.9	7.8 ± 5.0	4.3 ± 2.9	<0.01
Total Abnormalities	30.7 ± 14.9	31.7 ± 8.9	30.8 ± 16.1	0.20
2 Gy XRT/100μM HC
Chromosome Breaks	46.3 ± 29.3	46.4 ± 22.7	61.1 ± 32.6	0.052
Chromatid Breaks	26.1 ± 11.8	20.2 ± 8.9	25.9 ± 15.1	0.16
Fusion Events	8.7 ± 6.7	9.5 ± 6.1	8.8 ± 7.2	0.36
Total Abnormalities	81.1 ± 45.1	76.1 ± 23.1	95.8 ± 44.2	0.08