[Products of exocrine secretion of the breast and breast cancer]

The breast is an exocrine gland which secretes the proteins present in breast milk, such as casein and lactalbumin. The apocrine metaplasia which often accompanies cystic transformation may result in the production of proteins in the cystic fluid: GCDFP (Gross cystic disease fluid protein). The production of these proteins by breast cancer and their secretion into the blood enable them to be considered as markers of tumour differentiation. They are useful to the clinical oncologist as quantifiable parameters of tumour extension and response to treatment. In the future, they may provide an index of malignant transformation and hormone dependence.