Relationship between rate of posterior uveal melanoma flattening following plaque radiotherapy and gene expression profile class of tumor cells

Purpose. To evaluate the relationship between rate of flattening of posterior uveal melanomas (PUMs) over the first 6 months following I-125 plaque radiotherapy and gene expression profile (GEP) class of tumor cells obtained by fine needle aspiration biopsy (FNAB) prior to treatment. Methods. Retrospective analysis of relationship between GEP of PUM cells obtained by FNAB at or prior to treatment and rate of tumor flattening following I-125 plaque radiotherapy. Impact of initial tumor thickness was minimized by pairing cases so baseline tumor thickness in subgroups was matched to within ± 0.5 mm. Paired t-testing compared mean tumor thickness in GEP subgroups at 3- and 6-months post treatment assessments. Results. Our initial group consisted of 269 patients. Seventy-seven tumors (28.6%) were GEP class 2. Twenty-seven of these were treated by I-125 plaque radiotherapy post-FNAB and returned for post treatment evaluations at 3 and 6 months. A matched GEP class 1 tumor was identified for 25 class 2 cases. Matched tumor pairs ranged in thickness from 2.5 to 11.5 mm at baseline. Mean tumor thickness at baseline in the GEP 1 subgroup was 5.8 and 5.9 mm in the GEP 2 subgroup. Three-months post plaque, mean tumor thickness was 4.5 mm in class 1 cases and 4.6 mm in class 2 cases (paired t 1/4 0.31, P 1/4 0.76). The 6-month post-plaque, mean tumor thickness was 4.0 mm in each subgroup (paired t 1/4 0.25, P 1/4 0.81). Conclusions. Our study showed a lack of association between the GEP class and the rate of flattening of posterior uveal melanomas following I-125 plaque radiotherapy of PUMs.