Endocrine Abstracts

Pain due to bone metastases can be relieved by local radiotherapy (RT). The mechanism of pain relief by RT has not been fully elucidated. Inhibition of bone resorption has been proposed as a possible mechanism. Osteoprotegrin (OPG) has been shown to block behaviours indicative of pain in mice with bone metastases and to diminish bone destruction (Honore et al., 2000, Nature Medicine 6; 521–8).

The aim of this study was to evaluate serum OPG levels in patients with metastatic bone pain following RT. The hypothesis is that an increase in OPG production following RT might be responsible for inhibition of bone resorption and thus of pain relief.

Sixteen patients with bone metastases were studied after obtaining an ethical committee approval. Blood was collected at baseline (prior to RT), and weekly for 4 weeks after RT for measurement of OPG using ELISA Kits (Biomedica Gruppe). As a bone resorption marker, C-terminal cross-linked telopeptide of type I collagen (CTX) was also measured. Similarly, pain assessment scores were recorded (McGill Pain Questionnaire and Visual Analogue Scale).

Thirteen patients (81%) had pain relief 4 weeks after RT (responders), while 3 (19%) were non-responders. There was no significant difference in mean OPG levels between pre RT and I, 2, 3 and 4 weeks post RT in both responders (103.7±13.6, 114.1±17.2, 105.7±17, 114.7±21.7, 110.2±17.9 pg/ml) (P>0.05 for all intervals), and non-responders (113.3±20.67; 115±42; 105.7±18.1, 93.5±7.5 and 84.5±9.5 pg/ml) respectively. Likewise, there was no significant change in mean CTX level before and after RT in both responders and non-responders.

In conclusion, there was no correlation between circulating OPG levels and pain relief following RT.