Complete cDNA Sequencing of p53 Gene May Reveal Important Prognostic Information for Breast Cancer Patients

DNA sequence analysis of the p53 gene may provide informationabout the response to therapy for breast cancer patients, accordingto a study presented by Jonas Bergh, MD, associate professor ofoncology, at the annual meeting of the American Society of ClinicalOncology. The study represents the first complete sequencing ofthe p53 gene in a large retrospective study of a population basedcohort. Previous studies have focused primarily on exons 5, 6,7, and 8, using techniques such as single strand conformationpolymorphism (SSCP) to screen for mutations, followed by sequencingonly to verify identified mutations. Since mutations are foundover the entire coding sequence, some could be missed using traditionalprotocols.

Mutations of the p53 gene are considered to be a critical stepin the development of human malignancies, including breast cancer.These alterations can be determined using immunohistochemistrytechniques or DNA analysis, which can reveal prognostic information.

Conducted at the Uppsala Akademiska University Hospital in Swedenin cooperation with Pharmacia Biotech's molecular systems division,and the support of the Swedish Cancer Society, the study's objectivewas to analyze the associations between mutations and outcomeusing a cDNA sequencing technique. Further, the study was designedto demonstrate the use of automated DNA sequencing of the completep53 gene to process large numbers of samples.

Frozen tumor material from a total of 317 consecutive Scandinavianwomen, operated on for breast cancer from January 1987 throughDecember 1989, was analyzed by means of a complete cDNA sequencingof the p53 gene and a total of 69 mutations were discovered.

97 patients had primary lymph node metastases while 206 were codenegative. In 14 cases, the node status of the patient was unknown,since axillary exploration was not performed. The median followup time was 58 months.

Study findings demonstrated that mutations of the p53 gene identifieda group of patients with worse prognosis. The study also founda correlation between the location of the p53 mutation and theprognosis of node negative and node positive breast cancer patients.As with other studies, these findings require review and verificationby the scientific community.