Glycoproteins, including Gross Cystic Disease Fluid Protein-15 antibody (GCDFP-15), are considered to be markers of apocrine differentiation. Numerous studies have shown GCDFP-15 to be a specific marker for breast cancer in formalin-fixed, paraffin-embedded tissues and in cytologic preparation (fine needle aspirates). Studies on breast cancer have shown that GCDFP-15 associated significantly with a profile of good prognosis tumors. Another breast cancer study showed that 73.3% of invasive breast carcinomas expressed GCDFP-15. Other types of tissues that express GCDFP-15 are axillary sweat glands and submandibular salivary glands.