PURPOSE: A gene expression signature, predictive for local recurrence after breast-conserving treatment, has previously been identified from a series of 165 young patients with breast cancer. We evaluated this signature on both another platform and an independent series, compared its performance with other published gene-sets, and investigated the gene expression profile of a larger data set.
EXPERIMENTAL DESIGN: Gene expression tumor profiles were obtained on 148 of the initial 165 Dutch patients and on an independent validation series of 195 French patients. Both unsupervised and supervised classifications were used to study the gene expression profile of the 343 breast cancers and to identify subgroups that differ for their risk of local recurrence.
RESULTS: The previous local recurrence signature was validated across platforms. However, when applied to the French patients, the signature did not reproduce its reported performance and did not better classify the patients than other published gene sets. Hierarchical clustering of all 343 breast cancers did not show any grouping reflecting local recurrence status. Genes related to proliferation were found differentially expressed between patients with or without local recurrence only in triple-negative tumors. Supervised classification revealed no significant gene set predictive for local recurrence or able to outperform classification based on clinical variables.
CONCLUSIONS: Although the previously identified local recurrence signature was robust on another platform, we were neither able to validate it on an independent data set, nor able to define a strong gene expression classifier for local recurrence using a larger data set. We conclude that there are no significant differences in gene expression pattern in tumors from patients with and without local recurrence after breast-conserving treatment.