Background Largest basal diameter (LBD) appears to have independent prognostic value in uveal melanoma (UM).

Methods All patients undergoing plaque brachytherapy or enucleation for UM involving the choroid and/or ciliary body between 2012 and 2019.

Results A total of 348 patients with a mean age of 60±14 years were included and followed for a mean of 40±26 months (3.3±2.2 years). On multivariate analysis, LBD >12 mm remained a significant independent predictor of metastasis for both class 1 (HR 21.90; 95% CI 2.69 to 178.02; p=0.004) and class 2 (HR 2.45; 95% CI, 1.03 to 5.83; p=0.04) tumours. Four prognostic groups were created: group 1 (class 1, LBD <12 mm), group 2 (class 1, LBD ≥12 mm), group 3 (class 2, LBD <12 mm) and group 4 (class 2, LBD ≥12 mm). Life tables were used to calculate the 3-year and 5-year metastasis-free survival: group 1 (98 and 98%), group 2 (86 and 86%), group 3 (81 and 62%) and group 4 (54 and 47%). Compared with the reference category (group 1), the Cox proportional hazard model demonstrated a significant worsening of survival for each progressive category (group 2 (HR 21.59; p=0.004), group 3 (HR 47.12, p<0.001), and group 4 (HR 114.24; p<0.001)). In our dataset, the four-category Cox model performed poorer compared with the American Joint Committee on Cancer (AJCC) and gene expression profile (AJCC+GEP) in the Akaike’s information criteria (AIC) (297 vs 291), fit better with the Bayesian information criteria (BIC) (309 vs 313) and performed similarly with the Harrel’s C (0.86 (95% CI 0.80 to 0.91) vs 0.89 (0.84 to 0.94), respectively).

Conclusions Combination of GEP and LBD allows separation of patients into four easy-to-use prognostic groups and was similar to a model combining AJCC stage with GEP.