ESR1 and osteosarcoma: 32 Estrogen receptor (ER)-β and progesterone receptor (PR) were present in the majority of osteosarcoma cases analyzed by Dohi et al.,33 but ER-α and aromatase were not detected. The same authors found that the proliferation of osteosarcoma cells was stimulated by estradiol and progesterone and suppressed by ER and PR blockers. Interestingly, Dominguez-Malagón et al.34 found negative expression of ER and PR in 95.24% and 100% of the cases of jaw-osteosarcoma, respectively.