Clinical tumour, treatment parameters predict regression of choroidal melanoma after brachytherapy
A number of clinical tumour and treatment parameters, most of which are shown to reflect initial tumour size, appear to contribute to the regression of choroidal melanoma after brachytherapy, a recent study has shown.
“An independent predictor of regression of tumor thickness was the isotope used. These two covariates need to be adjusted for when exploring the associations with the rate of regression of histopathologic or genetic features of the tumour,” the investigators said.
Faster regression, whether considering all tumours or those that regressed in a pattern compatible with exponential decay, was predicted by initial tumour thickness, largest basal diameter, ciliary body involvement, tumor–node–metastasis (TNM) stage, tumour shape group, break in Bruch’s membrane, having muscles detached and radiation dose to tumour.
Dark brown pigmentation predicted slower regression. Initial tumour thickness remained the predominant and robust predictor of tumour regression in multivariate modeling (p<0.0001).
Furthermore, use of ruthenium vs iodine isotope was found to be an independent predictor of faster regression of tumour thickness (p<0.018). For both isotopes considered alone, only initial tumour thickness clinically predicted regression (p<0.0001).
“Our model allows such future analyses efficiently without matching,” the investigators said.
The study analysed ultrasound images from 330 of 388 consecutive choroidal melanomas (87 percent) irradiated from 2000 through 2008 at a national referral centre in Finland. A 10-MHz B-scan was used to obtain images during 3 years of follow-up.
The investigators used a polynomial growth-curve function in a nested mixed linear regression model considering regression pattern and tumour levels to model the changes in tumour thickness and cross-sectional area.
Covariates included initial tumour dimensions, TNM stage, shape, ciliary body involvement, pigmentation, isotope, plaque size, detached muscles and radiation parameters.