Expression of aromatase and estrogen receptor alpha in chondrosarcoma, but no beneficial effect of inhibiting estrogen signaling both in vitro and in vivo

Background: Chondrosarcomas are malignant cartilage-forming tumors which are highly resistant to conventional chemotherapy and radiotherapy. Estrogen signaling is known to play an important role in proliferation and differentiation of chondrocytes and in growth plate regulation at puberty. Our experiments focus on unraveling the role of estrogen signaling in the regulation of neoplastic cartilage growth and on interference with estrogen signaling in chondrosarcomas in vitro and in vivo.

Methods: We investigated the protein expression of estrogen receptor alpha (ESR1), androgen receptor (AR), and aromatase in tumor specimens of various chondrosarcoma subtypes, and (primary) chondrosarcoma cultures. Dose-response curves were generated of conventional central chondrosarcoma cell lines cultured in the presence of 17β-estradiol, dihydrotestosterone, 4-androstene-3,17 dione, 4-hydroxytamoxifen, fulvestrant and aromatase inhibitors. In a pilot series, the effect of anastrozole (n = 4) or exemestane (n = 2) treatment in 6 chondrosarcoma patients with progressive disease was explored.

Results: We showed protein expression of ESR1 and aromatase in a large majority of all subtypes. Only a minority of the tumors showed few AR positive cells. The dose-response assays showed no effect of any of the compounds on proliferation of conventional chondrosarcoma in vitro. The median progression-free survival of the patients treated with aromatase inhibitors did not significantly deviate from untreated patients.

Conclusions: The presence of ESR1 and aromatase in chondrosarcoma tumors and primary cultures supports a possible role of estrogen signaling in chondrosarcoma proliferation. However, our in vitro and pilot in vivo studies have shown no effect of estrogen-signaling inhibition on tumor growth.