Imbalance of sex chromosomes, with gain of early‐replicating X, in human solid tumors

An imbalance of sex chromosomes was observed in several cases of solid tumors: colorectal, anal canal and breast carcinomas. Replication studies, using BUdR incorporation, show that in males there is a tendency towards a gain of early-replicating X and a deficiency of Y chromosomes. In females, there is a tendency towards a gain of early-replicating X and a loss of late-replicating X chromosomes. Although almost no replication studies have been published in the literature, making it impossible to distinguish between late- and early-replicating Xs, it is likely that a similar situation exists for several solid tumors other than those we have studied. A possible consequence of this imbalance is briefly discussed.