Association between Tumor Regression Rate and Gene Expression Profile after Iodine 125 Plaque Radiotherapy for Uveal Melanoma

Purpose Gene expression profile (GEP) testing segregates uveal melanoma (UM) into 2 main prognostic classes. It is unknown if a greater tumor regression response after iodine 125 (I¹²⁵) brachytherapy correlates with class 2 GEP status. The purpose of this study was to determine whether there is a significant relationship between the rate of UM height regression and GEP classification testing after I¹²⁵ plaque brachytherapy. Design Multicenter, retrospective cohort study. Participants Adult UM patients treated with I¹²⁵ plaque brachytherapy who had concurrent tumor biopsy at the time of surgery with a GEP test result from January 1, 2010 through June 30, 2014. Methods Baseline clinical data and GEP class assignments were obtained. The ultrasonographic tumor height was recorded at baseline and at 3, 6, 9, and 12 months and at the most recent final follow-up visits. Subanalysis of paired cases based on pretreatment ultrasound height was performed. Statistical analysis was performed using Wilcoxon rank-sum tests, the Fisher exact test, and Kaplan-Meier analysis. Main Outcome Measures Percentage change in tumor height from baseline. Results A total of 353 patients were included in the study. Median follow-up was 2.1 years (range, 0.5–5.3 years). Gene expression profile status was class 1 in 247 tumors (70%) and class 2 in 106 tumors (30%). Increased patient age, larger tumor dimensions, and greater tumor thickness were associated with class 2 GEP status (P = 0.006, P < 0.001, and P < 0.001, respectively). The percentage reduction in tumor height from baseline was significantly greater in class 1 than class 2 tumors at 3 months (17.5% vs. 11.8%; P = 0.007) and 6 months (26.8% vs. 17.1%; P = 0.007), respectively, but there was no significant difference in reduction between class 1 and 2 tumors at 9 months (P = 0.26) and 12 months (P = 0.57) after treatment. Class 1A and 1B tumors showed similar reduction compared with class 2 tumors (P < 0.05). Conclusions Class 1 UM tumors tend to regress more rapidly than class 2 tumors in the first 6 months after plaque radiotherapy. Class 1A and 1B tumors regress at similar rates after plaque radiotherapy.