P53 functional assay in yeast: evaluation in 1856 patients in a large prospective clinical trial (EORTC 10994/BIG 00-01).

CTRC-AACR San Antonio Breast Cancer Symposium: 2008 Abstracts Abstract #1067 Background:Although mutations in the p53 gene can occur in 20-30% of sporadic breast cancer, and are associated with other poor prognostic factors, there is no clear evidence as to whether p53 status should influence therapy. Immunohistochemistry has been demonstrated to be an inferior method compared with sequencing, but the optimal technique to assess the functional p53 status is not known. The yeast test is a functional assay which tests the transcriptional competence of p53, and detects biologically important mutations. Here we present the results of p53 evaluation using this method in a prospective study. Material and methods: EORTC 10994/BIG 00-01 trial is a randomized trial comparing the neoadjuvant use of an anthracycline-based regimen with a taxane-containing regimen in patients with large operable or locally advanced breast cancers. Fresh frozen tumour biopsies were mandatory before starting chemotherapy. Frozen sections were examined centrally and the p53 test was done if the invasive tumour cell content was above 20%. RNA extract was used to assess p53 status: p53 wild type tumours were defined as tumours whose cDNA transfected in yeast gave less than 20% red colonies (background); p53 mutated tumours gave 20% or more red colonies. Results: The trial accrual was completed in November 2006 after inclusion of 1856 patients. There was no frozen sample available in 70 patients. In 276 patients the % of tumour cells was <20. The p53 test failed in 62 patients, generally because the quality or quantity of RNA was too low for RT-PCR. P53 was successfully assessed in 1458 patients: 661 (45%) tumours are p53 mutated and 797 (55%) are p53 wt. p53 mutated and wild type tumours were grade III in 40% (265/661) and 19% (153/797), respectively, and estrogen receptor negative in 41% (270/661) and 14.5% (116/797), respectively. We did not see any correlation between p53 status and tumour size or nodal status at diagnosis. HER2 status data are being collected. Conclusion: P53 status has been successfully evaluated using a yeast assay in 78.5% (1458/1856) of cases in the context of a multicenter trial. In indirect comparisons the frequency of patients with functionally altered p53 status is higher than with sequenced based methods. Our results confirm an association between p53 mutation and high grade or estrogen receptor negative status, but not with age, tumour size or clinical nodal status. More data regarding the quality and quantity of RNA collected will be presented at the meeting. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 1067.