Abstract: This invention is directed to compositions and their uses for detection of markers. Such markers may be useful in the understanding of the underlying molecular event leading to a condition or a disease in a subject. These markers may also be useful for characterization of neoplastic cells and cancer cells and their response to certain therapeutical regimes. Therefore the invention as disclosed may contribute to the improvement of the stratification of patients for the best possible treatment.

Abstract: The present invention relates to methods for estimation of efficacy of therapeutic treatment of cancer patients, in particular breast cancer patients. The estimation is based on determining of the status of aberration of the estrogen receptor alpha gene (ESR1) in situ, and, optionally, the status of aberration of a gene related to ESR1. In particular, the invention relates to determining the presence or absence and, if present, the type of aberration, e.g. amplification, duplication, polyploidization, deletion or translocation of the ESR1 gene in the tumor cells of the patient. The invention further relates to a kit-in-parts comprising probes for the determining the status of aberration of ESR1 and ESR1-related genes in situ.