ESR1 and breast carcinoma: In breast carcinomas, the analysis of the AP-1 family members (c-jun, junB, junD and c-fos, fosB, fra1 and fra2) revealed association of fosB expression with a well-differentiated receptor-positive tumor phenotype, whereas the expression of fra-1 showed significant negative correlation with fosB expression, as well as with estrogen-receptor status and differentiation [16].