AbstractBased on the Barr body frequency, a total of 285 unselected breast cancer tissues were categorised as negative and positive tumours; incidence of these two groups in our series was 2:1, respectively. When 2‐years' disease‐free interval and 10‐years' survival were considered, it was seen that patients harbouring negative tumours had significantly early recurrence and shorter duration of survival as compared to those having positive tumours. As vascular spread is the prerequisite of early recurrence, the shorter survival in the patients having negative tumours could be explained on the basis of blood vessel invasion, in that 73% of the negative tumours had blood vessel invasion, in contrast to only 24% in the positive tu