Aim To determine the reduction of choroidal melanoma thickness 6 months after ruthenium 106-brachytherapy according to chromosome 3 status, which correlates strongly with metastatic death.

Methods Transscleral fine needle aspiration biopsy was performed prior to the insertion of a radioactive plaque if the tumour was deemed sufficiently thick and anterior for such a procedure. Transretinal biopsy with a 25-gauge vitreous cutter was performed for thin and posterior tumour within a month of plaque removal. The chromosome 3 status was determined by fluorescence in situ hybridisation from 2002 until 2006, and by either multiplex ligation-dependent probe amplification and/or microsatellite analysis after this period until the end of the study. The choroidal melanoma dimensions were obtained from outpatient visits.

Results 149 eyes from 149 patients were included. The mean age was 60.8 years. 84 eyes (56.4%) had disomy 3 and 65 eyes (43.6%) monosomy 3. The median pretreatment tumour thickness was 3.0 mm in disomy 3 and 4.1 mm in monosomy 3 tumours (p=0.018). The follow-up duration medians were 6.3 months for disomy 3 and 6.4 months for monosomy 3 tumours (p=0.68). The rates of thickness reduction were 6.7% and 7.0% per month, respectively (p=0.59). Thickness reduction exceeding 50% occurred in 32 (38.1%) disomy 3 and 24 (36.9%) monosomy 3 tumours.

Conclusions The rate of choroidal melanoma regression after ruthenium-106 brachytherapy does not appear to correlate with chromosome 3 loss, suggesting that tumour thickness reduction 6 months after treatment is unlikely to predict survival.