Table 1.

Characteristics of 27 283 women with early-stage breast cancer diagnosed between 1973 and 1989 and treated with adjuvant radiotherapy, stratified by left-sided versus right-sided cancer^*

Characteristic	Left-sided cancer	Right-sided cancer	P
No. of women	13998	13285
Age at diagnosis (mean±SD, y)	56.9±13.2	56.8±13.3	.47
Race/ethnicity
Non-Hispanic white	12347 (88.2)	11648 (87.7)	.63
Black	1017 (7.3)	1006 (7.6)
Asian	582 (4.2)	582 (4.4)
Other/unknown	52 (0.4)	49 (0.4)
Year of diagnosis
1973–1979	4451 (31.8)	4201 (31.6)	.52
1980–1984	3364 (24.0)	3131 (23.6)
1985–1989	6183 (44.2)	5953 (44.8)
Stage
In situ	460 (3.3)	458 (3.4)	.55
Localized	6299 (45.0)	5904 (44.4)
Regional	7239 (51.7)	6923 (52.1)
Length of follow-up (mean±SD, mo)	111.1±61.0	111.3±61.2	.77

^*Patient characteristics by left-sided versus right-sided disease were also compared stratified by the three time-of-diagnosis cohorts (1973–1979, 1980–1984, 1985–1989). There were no statistically significant differences between patients with left-sided and those with right-sided disease in any of the cohorts. P values were derived by using the chi-square test or t test, as appropriate. SD = standard deviation.