Background: It is often difficult to draw a firm conclusion as to whether the second breast cancer is primary or secondary (metastasis from the initial breast cancer) in a patient with metachronous bilateral breast cancer. In this study we have applied clonal analysis of breast cancer to distinguish whether the second breast cancer is primary or secondary.
Methods: A 54-year-old woman underwent modified radical mastectomy of the right breast as a result of breast cancer. Five years later she had tumors in the right chest wall and left breast. Fine-needle aspiration cytologic examination revealed that both tumors were adenocarcinoma. To elucidate the origin of these tumors, clonal analysis was done on DNA samples prepared from cryostat sections of the initial right breast cancer and from fine-needle aspirates of the tumors in the right chest wall and left breast. The method for clonal analysis was based on restriction fragment length polymorphism of X chromosome-linked phosphoglycerokinase gene and on differential methylation of the gene caused by random inactivation of one of two X chromosomes.
Results: Clonal analysis revealed that clonal origin of the right breast cancer was different from that of the left breast cancer and identical to that of the chest wall tumor. Therefore it was concluded that the left breast cancer was primary and the chest wall tumor was concluded that the left breast cancer was primary and the chest wall tumor was a recurrence of the initial breast cancer.
Conclusions: Clonal analysis appears to be a useful method in discriminating a primary from a secondary cancer.