We demonstrated previously that spontaneously Tam-resistant (TamR) derivatives of the MCF7 breast carcinoma cell line have constitutively phosphorylated Tab2, and knocking-down Tab2 expression by siRNA is sufficient to restore the antiproliferative response to Tam [8], thus implying constitutive activation of Tab2 in endocrine resistance. This evidence concerns the gene TAB2 and breast carcinoma.