Clonal analysis of predominantly intraductal carcinoma and precancerous lesions of the breast by means of polymerase chain reaction.

Clonality of predominantly intraductal carcinoma (PIC) and precancerous lesions of the breast was analyzed by a method based on restriction fragment length polymorphism of the X-chromosome-linked phosphoglycerokinase gene and on random inactivation of the gene by methylation. The application of polymerase chain reaction to this method enabled clonal analysis of small lesions. In order to eliminate the contamination by normal stromal cells, intraductal components were microdissected from the frozen sections of PIC under a dissection microscope. Clonal analysis of the intraductal components from seven PICs revealed that all were monoclonal in origin. In three PICs with intraductal spreading of carcinoma cells over nearly a whole breast gland, the intraductal components were collected from eight widely separated sites in each case. Clonal analysis of these samples showed that every sample was monoclonal and the same allele of the phosphoglycerokinase gene was consistently inactivated in each case. These results suggest that PIC arises as a single monoclonal carcinoma and spreads through the ducts over the gland rather than having multicentric origins. Clonality of precancerous lesions such as atypical ductal hyperplasia and intraductal papilloma arising in the terminal ducts was also studied. Intraductal components were microdissected from the paraffin sections of these lesions and subjected to clonal analysis. Both atypical ductal hyperplasia and intraductal papilloma were found to be monoclonal in origin, suggesting that certain genetic changes had already occurred in the precancerous lesions. A further study is needed to elucidate these genetic changes, which would greatly help our understanding of the mechanism of carcinogenesis.