The Novel RARβ Isoform (β 5) is a Potential Target of Retinoids in Breast Cancer

Retinoic acid receptor beta 2 (RARβ2) isoform has been considered a putative tumor suppressor because it is expressed in normal cells but is lacking in most tumors, including breast cancer. Recently, we identified a novel RARβ isoform (β5) in breast cancer cells, which may sereve as a potential target of retinoids in cancer prevention and therapy studies. In this review are summarized the data on the expression of RARβ5 and of the previously identified RARβ4 and RARβ' isoforms in various breast cancer cell lines. We found that RARβ5 may serve as a potential biomarker of resistance of breast cancer cells to retinoids and thus may have clinical implication in selecting patients that may benefit the most from clinical trials with retinoids.