Loss of heterozygosity, allele silencing and decreased expression of p73 gene in breast cancers: prevalence of alterations in inflammatory breast cancers

The p73 gene is a p53 homologue located at 1p36-33, a region submitted to deletions in breast cancer (BC) and putatively imprinted. To study whether p73 was associated with breast carcinogenesis, loss of heterozygosity (LOH), allele expression and transcript levels were assessed in 59 BC, including 39 BC presenting no inflammatory symptoms (NBC) and 20 inflammatory BC (IBC). IBC is a rare but aggressive form of cancer with a very poor prognosis. Normal breast epithelium (BE) and lymphocytes from patients were used as controls. StyI polymorphism generating GC and/or AT alleles was used to select 22 heterozygous patients. p73 LOH was significantly higher in IBC than in NBC [five of eight cases (62%) versus two of 14 cases (14%); Fisher's exact test, P=0.05]. p73 was biallelically expressed in all BE. In contrast, 12 of 16 (75%) BC were monoallelically expressed, showing that allele silencing was significantly associated with breast carcinogenesis (P=0.012), AT being the preferential silent allele (10 out of 12 tumours). p73 mRNA levels in NBC and IBC were two- and threefold lower than in BE, respectively, suggesting that decreased expression could be related to tumour aggressiveness. In conclusion, LOH, allele silencing and decreased expression of the p73 gene may play a role in breast carcinogenesis.