Breast cancer is the most common cancer in women. The development of breast cancer often originates from epithelial cells in the mammary gland – the very cells that specialise in milk production during and after pregnancy. A team of researchers from Friedrich Schiller University Jena (Germany), the university in Shenzhen (China) and Jena University Hospital (Germany) has taken a closer look at this specialisation process and deciphered a molecular mechanism that also appears to play an important role in cancer development. It may be possible to develop new diagnostic procedures and treatment methods for breast cancer based on these research findings.