Several small-scale studies suggest that at least thirty percent of the 189 tumors examined to date express variants of DNA polymerase beta (Pol beta) gene and none of these mutations are common polymorphisms. This suggests that there is a link between mutations in Pol beta and cancer. Preliminary data from our laboratory shows that expression of the cancer-derived I260M, K289M, and E295K Pol beta mutants in mouse cells results in cellular transformation. We have also shown that DNA synthesis by the K289M colon cancer-associated and I260M prostate cancer-associated Pol beta mutant enzymes results in the induction of mutations. These results demonstrate that Pol beta cancer- associated mutants have functional phenotypes. Because Pol beta is a key enzyme in the base excision repair pathway, our results suggest that abnormal base excision repair by Pol beta enzyme variants contributes to human cancers. These studies provide the impetus to determine whether mutations in the Pol beta gene make a significant contribution to human cancer. Because breast carcinoma is the second leading cause of cancer-related death in women, we are focusing on this disease. The broad long-term objectives of the proposed research are to determine if Pol beta is mutated in a high frequency of human breast tumors, to identify the types of Pol beta mutations in these tumors, and to determine if the Pol beta mutations we identify have a functional phenotype. These studies will be performed by determining the DNA sequences of the Pol beta gene from 300 breast tumors and comparing them to normal controls, to obtain the percentage of tumors that harbor Pol beta variants. The results will be compared to outcome data. The variants we obtain will be characterized in genetic and biochemical assays to determine if they have phenotypes that are consistent with cancer etiology. [unreadable] [unreadable] [unreadable]