Alterations of the FHIT gene in breast cancer: association with tumor progression and patient survival.

Our previous results on breast tumors show that LOH (loss of heterozygosity) at the FHIT locus is associated with reduced Fhit protein expression. We have also shown that LOH at this locus is significantly higher in tumors from patients carrying the BRCA2 999de15 mutation than in tumors without this mutation, presumably because of lack of DNA repair. Here, our aim was to determine the relationship of FHIT LOH with breast tumor progression. Five microsatellite markers located within the FHIT gene were typed in 239 breast tumors and corresponding normal tissue, and the LOH results were compared with clinicopathologic factors and LOH at other chromosome regions. LOH at FHIT is associated with estrogen- and progesterone-negative breast tumors, high S-phase fraction, reduced patient survival, and LOH at chromosome regions 6q, 7q, 8p, 9p, 11p, 11q, 13q, 16q, 17p, 17q, 18q, and 20q. A multivariate analysis shows that LOH at FHIT results in a 60% increased relative risk of dying. We conclude that the loss of FHIT results in growth advantage of breast tumor cells, is associated with unstable genome, and may be of prognostic value.

Analysis of the fragile histidine triad (FHIT) gene in lobular breast cancer.

The fragile histidine triad (FHIT) gene is a candidate tumour suppressor gene in breast and other cancers. We investigated deletions within the FHIT gene in lobular breast cancer and found that 16% of cases showed loss of heterozygosity (LOH) within the gene. We compared LOH within FHIT in lobular and ductal breast tumours and found a significant association between LOH at FHIT and the ductal histological type (P<0.001). To determine whether genomic alteration of the FHIT gene in lobular breast cancer leads to Fhit inactivation we have assessed the level of Fhit expression by immunohistochemical detection and determined that 27% (15 of 55) consecutive sporadic lobular tumours showed negative or reduced Fhit expression. A significant association was found between LOH at the FHIT gene and reduced Fhit expression in lobular and ductal tumours (P=0.025 and P=0.001, respectively). Thus, genetic alterations within the FHIT gene, leading to loss of Fhit protein, may play an important role in the carcinogenesis of a significant number of sporadic lobular breast cancers, even though the apparent frequency of genomic alterations within the gene is lower than in ductal breast cancer.

Chromosome 8p alterations in sporadic and BRCA2 999del5 linked breast cancer.

Chromosomal losses involving the short arm of chromosome 8 are frequent in a variety of tumour types, including breast cancer, suggesting the presence of one or more tumour suppressor genes in this region. In this study, we have used 11 microsatellite markers to analyse loss of heterozygosity (LOH) at chromosome 8p in 151 sporadic breast tumours and 50 tumours from subjects carrying the BRCA2 999del5 mutation. Fifty percent of sporadic tumours compared to 78% of BRCA2 linked tumours exhibit LOH at one or more markers at 8p showing that chromosome 8p alterations in breast tumours from BRCA2 999del5 carriers are more pronounced than in sporadic breast tumours. The pattern of LOH is different in the two groups and a higher proportion of BRCA2 tumours have LOH in a large region of chromosome 8p. In the total patient material, LOH of 8p is associated with LOH at other chromosome regions, for example, 1p, 3p, 6q, 7q, 9p, 11p, 13q, 17p, and 20q, but no association is found between LOH at 8p and chromosome regions 11q, 16q, 17q, and 18q. Furthermore, an association is detected between LOH at 8p and positive node status, large tumour size, aneuploidy, and high S phase fraction. Breast cancer patients with LOH at chromosome 8p have a worse prognosis than patients without this defect. Multivariate analysis suggests that LOH at 8p is an independent prognostic factor. We conclude that chromosome 8p carries a tumour suppressor gene or genes, the loss of which results in growth advantage of breast tumour cells, especially in carriers of the BRCA2 999del5 mutation.

Reduced Fhit expression in sporadic and BRCA2-linked breast carcinomas.

Evidence for alteration of the FHIT gene in a significant fraction of breast carcinomas has been reported, in apparent concordance with loss of heterozygosity (LOH) at chromosome region 3p14.2 in breast cancer and benign proliferative breast disease. A significantly higher frequency of LOH at the FHIT locus was reported for BRCA2-/- tumors, possibly due to misrepaired double-strand breaks at this common fragile region. To determine whether such genomic alterations lead to Fhit inactivation, we have assessed the level of Fhit expression by immunohistochemical detection in sporadic tumors and cancers occurring in BRCA2 999del5 carriers. To determine whether Fhit inactivation may have prognostic significance, we have also assessed expression of breast cancer markers and clinical features in sporadic tumors relative to Fhit expression. Of 40 consecutive sporadic breast carcinomas studied for tumor markers, 50% showed reduced Fhit expression. In these sporadic cancers, loss of Fhit expression was not correlated significantly with the presence or absence of other tumor markers. In a study of 58 sporadic and 34 BRCA2 999del5 Icelandic invasive cancers, there was a significant association of LOH at 3p14.2 with reduced expression of Fhit (P = 0.001); also the lower expression of Fhit and higher LOH at 3p14.2 in BRCA2 999del5 tumors relative to sporadic cancers was significant (P = 0.002). Thus, genetic alteration at the fragile site within the FHIT gene leads to loss of Fhit protein in a significant fraction of sporadic breast cancers and a much larger fraction of familial breast cancers with an inherited BRCA2 mutation, consistent with the idea that loss of BRCA2 function affects stability of the FHIT/FRA3B locus.

High incidence of loss of heterozygosity in breast tumors from carriers of the BRCA2 999del5 mutation.

Germ-line mutation in the BRCA2 gene confers an increased risk of breast cancer. An elevation of additional genetic defects in tumors of patients with germ-line mutation in the BRCA2 gene compared with sporadic breast tumors has been reported. To evaluate the nature of the difference, we did detailed mapping of chromosomes 1p, 3p, 6q, 11, 13q, 16q, 17, and 20q, using microsatellite markers. We found that the frequency of loss of heterozygosity was similar at some chromosomal regions in the BRCA2 999del5 and sporadic tumors but significantly different at others. These others include chromosomal arms 3p, 6q, 11p, 11q, 13q, and 17p. Loss of heterozygosity mapping suggests that the same chromosome regions are involved in both tumor groups but at elevated frequencies in BRCA2 999del5 tumors. This higher frequency of genetic aberrations could pinpoint genes that selectively promote tumor progression in individuals predisposed to breast cancer due to the BRCA2 999del5 germ-line mutation. Accumulation of somatic genetic changes during tumor progression may follow a specific and more aggressive pathway of chromosome damage in these individuals.