In more than 200 malignant human breast tumors examined (Invasive ductal carcinoma, Medullary carcinoma, Phyllodes sarcoma, Mucinous carcinoma, lobular carcinoma in situ and squamous cell carcinoma) 95% of both proteins were significantly overexpressed and 100% had either Fra-1 or c-Fos overexpressed contrasting with their undetectable levels in normal tissue. Here, FOS is linked to breast carcinoma.