c-myc proto-oncogene amplification seems to have a prognostic value in breast cancer. In this study, quantitative analysis of c-myc amplification was carried out by differential polymerase chain reaction technique (d-PCR) using beta-globin as the reference gene. d-PCR assessment showed coampIification products of c-myc and beta-globin depend on variations in reaction factors such as the genomic DNA concentration, the relative concentrations of the various amplimers, the thermostable DNA polymerase concentration and the number of cycles. However, amplification of c-myc can be estimated quantitatively. In addition, results of individual sets of d-PCR can be expressed on a standard reference scale. A clinical study of 309 patients with breast cancer found c-myc amplification, respectively in 19% (45/236) of primary tumour tissues, 21% (4/19) of subsequent second primary cancers, 36% (4/11) of tumours of patients with bilateral lesions, 40% (8/20) of local recurrence tumours and 22% (5/23) of metastatic lesions. Amplification of c-myc was observed more frequently in histological grades 2-3 (p<0.02), in ER negative (p<0.01) and PgR negative tumours (p<0.02), but was not associated with age, tumour size, nodal status, histology, cytosolic cathepsin D or pS2. d-PCR appears amenable to automation and should facilitate large scale, inter laboratory gene amplification studies.

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