In this Special Issue, authors from nine countries on five continents provide overviews on and insights into current research topics related to the 'Genetic Complexity of Hormone-Sensitive Cancers'. The chapters cover topics on completely novel technologies and instruments revolutionizing our view of biological entities, and also, novel extensions and revisions of existing and well-established technologies such as genetic probes and bar-coding techniques, which add a new dimension to microscopy, as they allow us to visualize DNA sequences and mRNA in situ. With this Special Issue, the editors wanted to create a forum for the international biomedical research community to compile their data on the genetic complexity of cancer in a unique resource. While this collection of articles cannot certainly claim completeness in any way, it represents an attractive collection of the different aspects of hormone-dependent cancers and will hopefully encourage further targeted research.