Cell-cell adhesion, as mediated by the cadherin-catenin system, is a prerequisite for normal cell function and the preservation of tissue integrity. With recent progress in our understanding, beta-catenin as a component of a complex signal transduction pathway may serve as a common switch in central processes that regulate cellular differentiation and growth. The function of the cadherin-catenin system in cell adhesion as well as in intracellular signaling, appears to be subjected to multifactorial control by a variety of different mechanisms, and data on a hormonal control of these signaling pathways, even though scarce to date, suggest an important regulatory influence in many cellular systems. Loss of E-cadherin-catenin function was described in many tumors along with an increased invasiveness and a decreased prognosis of many carcinomas, including tumors of endocrine glands and their target systems, and a causal role of this loss-of-function in the multifactorial process of tumorigenesis was recently proven in genetic mouse models. Modification of E-caderin-catenin function in endocrine and nonendocrine tumors may involve germline and somatic gene mutations, epigenetic mechanisms such as gene silencing due to promotor-hypermethylation, and posttranscriptional events, likely to be involved in many endocrine tissues and their target organs. Such events may converge on nuclear activation of oncogenes such as c-myc by the beta-catenin/TCF4 complex. The expression and functional status of the components of the cadherin-catenin system may serve as prognostic markers for endocrine and nonendocrine tumors. The frequent involvement of functional dysregulation in many tumors raises hopes that better definition of the regulation of all components of the cadherin-catenin system and their response to extracellular modulators may eventually lead to new therapeutic approaches for these tumors and help to prevent, more specifically, growth, invasion, and metastasis of these carcinomas.