The sarcoglycan complex, consisting of α-, β-, γ-, δ- and ε-sarcoglycans, is a multimember transmembrane system providing a mechanosignaling connection from the cytoskeleton to the extracellular matrix. Whereas the expression of α- and γ-sarcoglycan is restricted to striated muscle, other sarcoglycans are widely expressed. Although many studies have investigated sarcoglycans in all muscle types, insufficient data are available on the distribution of the sarcoglycan complex in nonmuscle tissue. On this basis, we used immunohistochemical and RT-PCR techniques to study preliminarily the sarcoglycans in normal glandular breast tissue (which has never been studied in the literature on these proteins) to verify the effective wider distribution of this complex. Moreover, to understand the role of sarcoglycans, we also tested samples obtained from patients affected by fibrocystic mastopathy and breast fibroadenoma. Our data showed, for the first time, that all sarcoglycans are always detectable in all normal samples both in epithelial and myoepithelial cells; in pathological breast tissue, all sarcoglycans appeared severely reduced. These data demonstrated that all sarcoglycans, not only β-, δ-, and ε-sarcoglycans, have a wider distribution, implying a new unknown role for these proteins. Moreover, in breast diseases, sarcoglycans containing cadherin domain homologs could provoke a loss of strong adhesion between epithelial cells, permitting and facilitating the degeneration of these benign breast tumors into malignant tumors. Consequently, sarcoglycans could play an important and intriguing role in many breast diseases and in particular in tumor progression from benign to malignant.