Purpose
Several retrospective clinical studies prior to the advent of gene expression profile (GEP) testing of posterior uveal melanomas showed faster rate of flattening of the tumor over the first 6 months following focal radiotherapy to be predictive of significantly higher actuarial probabilities of death from metastasis. To date, there have been no reports describing the relationship between GEP class of tumor cells obtained by FNAB prior to primary tumor treatment and post-treatment tumor regression following plaque radiotherapy. We hypothesized that GEP class would be strongly associated with faster tumor shrinkage post-plaque.
Methods
Retrospective analysis of the relationship between GEP class of posterior uveal melanoma cells and rate of post-irradiation tumor flattening during the first 6 post-treatment months in patients managed by I-125 plaque radiotherapy and evaluated by FNAB at or shortly prior to the start of treatment. To minimize the impact of initial tumor thickness on rate of tumor flattening, we employed a paired case approach in which tumor thickness at baseline in class 1 and class 2 cases was matched to within ± 0.5 mm. Paired t-testing was used to compare the mean thickness of the tumors in the GEP subgroups at the 3 and 6 month post-treatment assessments.
Results
Our base study group (9/7/07 - 4/27/12) consisted of 269 patients. 77 of these tumors (28.6%) were GEP class 2. Thirty-seven of these 77 patients were treated by I-125 plaque radiotherapy post-FNAB and returned for ultrasonographic measurement of tumor thickness at both 3 and 6 months post-treatment. We identified a matching patient from the GEP class 1 tumor cases for each of the class 2 cases. The tumors in the 37 pairs of patients ranged in thickness from 2.0 mm to 11.0 mm at baseline. The mean tumor thickness was 5.6 mm in both GEP subgroups at baseline. At 3 months post-plaque, mean tumor thickness was 4.1 mm in the class 1 cases and 4.5 mm in the class 2 cases (paired t = 0.88, P = 0.061). At 6 months post-plaque, mean tumor thickness was 3.5 mm in the class 1 cases and 3.9 mm in the class 2 cases (paired t = 1.66, P = 0.11).
Conclusions
Association with GEP class of tumor cells does not appear on the basis of this study to explain the previously reported unfavorable prognostic impact of faster tumor flattening following focal irradiation of posterior uveal melanomas.
Keywords: 589 melanoma •
671 radiation therapy •
462 clinical (human) or epidemiologic studies: outcomes/complications