Endocrine Abstracts

Radiotherapy (RT) may represent a useful tool in the treatment of GH-secreting tumours in the presence of a post-operative active disease and single dose stereotactic RT/gamma knife is the preferred option in most cases. The effects of RT on the control of hormone secretion are very slow and pharmacological treatment remains necessary for years. Some authors advocate withdrawal of somatostatin analogues (SSA) during RT, although the short-term effects of RT on hormone secretion have been poorly studied. To address this issue, we used GH₃ cells as a model of GH-secreting tumours to evaluate the acute endocrine effects of a single irradiation dose.

Methods: GH₃ cells were treated with a LINAC and single 5 and 10 Gy irradiation were evaluated after 6, 24, 72 and 144 h in terms of cell proliferation and GH/PRL secretion/gene transcription by ELISA/Real Time RT-PCR assays.

Results: A significant time- and dose- dependent reduction of cell proliferation was observed in irradiated cells vs controls. In contrast, a significant time- and dose-dependent increase of GH and PRL release (ng/10⁶ cells) was observed after 72 and 144 h in irradiated cells (up to five- and 11-fold at 10 Gy, respectively, P<0.0001 vs controls). A progressive time-dependent increase in PRL gene transcripts was observed in both irradiated and control cells, with a modest increase in irradiated vs control cells at 6 and 24 h. GH transcription also tended to increase immediately after irradiation, but was markedly reduced in irradiated cells at 72 and 144 h (P<0.0001 vs controls), suggesting a predominant effect of RT on GH release.

Conclusion: Transient increases in hormone secretion may occur after irradiation of GH/PRL-secreting cells, with potential differential effects in hormone synthesis and release. Such data should be evaluated in clinical practice in order to reconsider the indications for SSA withdrawal before irradiation in acromegalic patients.