IntroductionWith the improvement of therapeutic options for the treatment of breast cancer, the development of brain metastases has become a major limitation to life expectancy in many patients. Therefore, our aim was to identify molecular markers associated with the development of brain metastases in breast cancer.MethodsPatterns of chromosomal aberrations in primary breast tumors and brain metastases were compared with array-comparative genetic hybridization (CGH). The most significant region was further characterized in more detail by microsatellite and gene-expression analysis, and finally, the possible target gene was screened for mutations.ResultsThe array CGH results showed that brain metastases, in general, display similar chromosomal aberrations as do primary tumors, but with a notably higher frequency. Statistically significant differences were found at nine different chromosomal loci, with a gain and amplification of EGFR (7p11.2) and a loss of 10q22.3-qter being among the most significant aberrations in brain metastases (P < 0.01; false discovery rate (fdr) < 0.04). Allelic imbalance (AI) patterns at 10q were further verified in 77 unmatched primary tumors and 21 brain metastases. AI at PTEN loci was found significantly more often in brain metastases (52%) and primary tumors with a brain relapse (59%) compared with primary tumors from patients without relapse (18%; P = 0.003) or relapse other than brain tumors (12%; P = 0.006). Loss of PTEN was especially frequent in HER2-negative brain metastases (64%). Furthermore, PTEN mRNA expression was significantly downregulated in brain metastases compared with primary tumors, and PTEN mutations were frequently found in brain metastases.ConclusionsThese results demonstrate that brain metastases often show very complex genomic-aberration patterns, suggesting a potential role of PTEN and EGFR in brain metastasis formation.

No abstract

Metastatic breast cancer remains essentially incurable, with mortality being especially high in patients who develop brain metastases. Approximately 15% of all epithelial tumors metastasize to the brain, with incidence rates highly dependent on the primary tumor type. Whereas colorectal cancer very seldom metastasizes to the brain (1–5%), breast cancer (15–20%) commonly metastasizes to the brain. Apparently, the brain microenvironment is specifically permissive for the growth of disseminated tumor cells from some carcinomas but not others. It is unknown by what mechanism the metastatic tumor cells adapt to the selection pressure exerted by the brain microenvironment. In this study we wanted to identify molecular breast tumor markers associated with metastatic spread to the brain. The CGH array profiles of 30 tumors from primary breast cancer patients were compared to 10 tumors of brain metastases from breast cancer cases. Copy number changes were found in all samples, and every chromosome arm (X chromosome and acrocentric short arms were excluded from the analysis). Overall, the CGH results of the primary breast tumors were in agreement with those described before. The brain metastases showed in general similar aberration patterns as the primary tumors. However, in the brain metastases a notably higher frequency of gains and losses could be found almost at every chromosome locus. Only gain of 1p and loss of 16q described as favorable markers for breast cancer were more common in the primary tumors. Statistically significant (multiarray p-value &lt;0.05) differences were found at 18 different chromosomal loci, nine loci were significantly more often lost and 7 loci gained in the brain metastases. Gains of 2q32-33 and 11q14-q21 and loss of most of chromosome 10q were unique findings to the brain metastases. Furthermore, an amplification of EGFR was found in 30% and a gain in 20% of the brain metastases, whereas 0% had an amplification and only 9.4% of the primary tumors showed a gain of EGFR. The aberration patterns of 10q and EGFR was verified by FISH and LOH analysis. In general, no major difference in the number and distribution of the high-level amplifications (20 loci in primary tumors and 11 in brain metastases) could be found between the primary and metastatic tumors. Most of the amplifications were unique to only one case, with only 5 loci in common for both primary tumors and metastases and 11 loci found in more than one cases. In conclusion, the results show a similarity of genetic aberration patterns between primary and metastatic tumors, i.e. the metastases carried the majority of the genetic alterations present in the corresponding primary tumors but with a significantly higher frequency. This would imply that brain metastases have occurred at a late stage of cancer progression. However, specific aberrations like gain of 2q and loss of 10q could almost exclusively be found in the metastases. Some of these markers could be useful to define a subgroup of high-risk patients and might have implications for their treatment management. Citation Information: Clin Cancer Res 2010;16(7 Suppl):B6