DNA sequence analysis of the p53 gene may provide information about the response to therapy for breast cancer patients, according to a study presented by Jonas Bergh, MD, associate professor of oncology, at the annual meeting of the American Society of Clinical Oncology. The study represents the first complete sequencing of the p53 gene in a large retrospective study of a population based cohort. Previous studies have focused primarily on exons 5, 6, 7, and 8, using techniques such as single strand conformation polymorphism (SSCP) to screen for mutations, followed by sequencing only to verify identified mutations. Since mutations are found over the entire coding sequence, some could be missed using traditional protocols.
Mutations of the p53 gene are considered to be a critical step in the development of human malignancies, including breast cancer. These alterations can be determined using immunohistochemistry techniques or DNA analysis, which can reveal prognostic information.
Conducted at the Uppsala Akademiska University Hospital in Sweden in cooperation with Pharmacia Biotech's molecular systems division, and the support of the Swedish Cancer Society, the study's objective was to analyze the associations between mutations and outcome using a cDNA sequencing technique. Further, the study was designed to demonstrate the use of automated DNA sequencing of the complete p53 gene to process large numbers of samples.
Frozen tumor material from a total of 317 consecutive Scandinavian women, operated on for breast cancer from January 1987 through December 1989, was analyzed by means of a complete cDNA sequencing of the p53 gene and a total of 69 mutations were discovered.
97 patients had primary lymph node metastases while 206 were code negative. In 14 cases, the node status of the patient was unknown, since axillary exploration was not performed. The median follow up time was 58 months.
Study findings demonstrated that mutations of the p53 gene identified a group of patients with worse prognosis. The study also found a correlation between the location of the p53 mutation and the prognosis of node negative and node positive breast cancer patients. As with other studies, these findings require review and verification by the scientific community.