SRC and breast cancer: However, an immunohistocytochemical analysis of breast cancer tissues, comparing antibodies recognizing either total SFK protein levels, or active SFKs (i.e., SFKs phosphorylated at Y416), indicated that it is specifically markers of Src activity that are highly correlated with breast tumour malignancy, while total levels of Src protein are not correlated (Elsbergeret al., 2010).