Pathologic Features of Tumor Activity and Stability in Uveal Melanoma Specimens after Fractionated CyberKnife Radiosurgery

To evaluate uveal melanoma cell activity and pathologic features after stereotactic CyberKnife radiosurgery in specimens from five patients. Specimens from five patients treated by CyberKnife radiosurgery in three fractions were included in this study. Because of persistent retinal detachment in 3 patients, tumour endoresection was performed at four, seven and ten month after CyberKnife radiosurgery. At nine and twelve months after treatment, enucleation of the eye globe was performed in 2 patients because of secondary tumour bleeding and missing regression. After histomorphological analysis and determination of Ki67-proliferation index, DNA cytophotometry, fluorescence in-situ hybridization evaluation for chromosome 3 loss, GNA11and GNAQ mutation analysis were performed. Four of the five tumours included in this study showed variable radiation-induced morphologic changes in the form of enlargement of cells and nuclei, cytoplasmic vacuolisation and nuclear fragmentation. The DNA content of a large fraction of tumour cells was hypoploid. On the other hand, single strikingly hyperchromatic melanoma cells showed marked aneuploidy. The proliferation fraction in the three endoresected tumours was very low (<1%), but it was elevated in the enucleation cases. Monosomy 3 was detected in two of the endoresection cases, but none of the enucleation cases. None of the patients experienced a local tumour recurrence, but two of the patients developed liver metastasis. Many melanoma cells seemed to be vital within the first 6 months after CyberKnife radiosurgery, but obvious radiation-induced morphologic changes, including tumour necrosis, hypoploid DNA content plus low Ki-67 index could indicate sublethal cell damage.