Increased sister chromatid exchange frequency in young women with breast cancer and in their first-degree relatives.

The well-known increased risk of breast cancer (BC) in first-degree relatives of patients with BC has been related to shared genetic factors including defective DNA repair, with loss of genomic integrity. On the other hand, it can be hypothesized that early-onset breast cancer is also associated with overburden of heritable factors leading to increased DNA injury. In this respect, we analyzed sister chromatid exchange frequency (SCE) in 20 women with breast cancer (all < or =40 years old), in their first-degree female relatives, and in 20 age-matched healthy females without a personal or family history of cancer. SCE was significantly increased (P < 0.05) in patients (7.17 +/- 1.81 per metaphase) and in their first-degree relatives (6.44 +/- 0.98), compared with controls (5.85 +/- 0.72). There was no difference in SCE frequency between patients and their first-degree relatives. We suggest that the increased SCE in patients reflects a genomic instability that may be operative in carcinogenesis. Further, genomic instability is shared also by first-degree relatives, although none of them had a history of breast cancer at the time of the study.