Relating genotype and phenotype in breast cancer: An analysis of the prognostic significance of amplification at eight different genes or loci and ofp53 mutations

Breast cancer heterogeneity can be related directly to its variability at t he genetic level. Thus, tumor genotyping could be a valuable approach to de fine breast tumor subtypes, It has been shown that it is possible to deline ate subgroups of breast tumors according to specific sets of DNA amplificat ions. The aim of the present work was to study the prognostic significance of these DNA amplifications. We studied DNA amplification at eight genes or loci (AIB1, CCND1, EMS1, ERBB2, FGFR1, MDM2, MYC, and RMC20C001) as well a s p53 mutations in a series of 640 breast cancer patients who had not recei ved presurgical therapy and analyzed the correlations with survival. DNA am plification was assessed by Southern blotting and was scored positive when exceeding three to five copies. Mutations in the p53 gene were searched by four-color fluorescent single-strand conformational polymorphism, using an automated sequencer. Of the nine genetic alterations tested, four (CCND1, E MS1, FGFR1, and p53 mutations) showed a significant association with reduce d disease-free (DFS) and/or overall survival (OVS) in the unselected set of patients by univariate test. Correlations for p53 were found only when sel ecting mutations in exons 5 or 7. Analysis of node-negative and -positive s ub-groups of patients showed that MDM2 amplification and p53 mutations bore prognostic significance in node-negative patients, whereas amplification o f CCND1, EMS1, and FGFR1 correlated with poor outcome in node-positive pati ents. Multivariate analysis on an unselected set of patients retained signi ficance for the amplification of EMS1, FGFR1, and MDM2 with DFS, of CCND1 w ith OVS, and of RMC20C001 with both DFS and OVS. Interestingly, stratified analysis according to nodal status confirmed results obtained in the univar iate tests: significance of MDM2 amplification and p53 mutations in node-ne gative and that of CCND1, EMS1, and FGFR1 in node-positive patients. We als o observed an association between the number of genetic alterations observe d in a tumor and poor prognosis. Patients with two or more amplified loci h ad a worsened outcome. Strongly correlating coamplifications such as CCND1 and FGFR1, as well as ERBB2 and MYC, were associated with a significant red uction of patient survival, thus indicating cooperative effects, Our data s upport the idea that genetic alterations in breast cancer are not only help ful for phenotyping purposes, but can also represent powerful prognostic in dicators in the clinical practice.