3.4 Absent tumor infiltrating lymphocytes is associated with worse progression free survival
Next, we sought to investigate the prognostic value of TIL status on PFS in stage I and II melanoma patients. We initially generated a Kaplan-Meier PFS curve stratifying patients by TILs present (both brisk and non-brisk) and TILs absent (Fig. 2 ). Absence of TILs was associated with significantly worse PFS (p=0.044). 5-year PFS was 78.2% for the TILs present group and only 33.3% for the TILs absent group. It should be noted that only 10 patients in our study had absent TILs.
We then performed a similar analysis but stratified TIL status by present-brisk, present-non brisk, and absent (supplementary information ). Because the majority of patients had present-non brisk TILs (n=45, 72.6%), we could not identify a significant difference between these groups.
Univariable Cox-proportional hazard models were generated for the biopsy variables listed in Table 4 . Tumor depth and ulceration were the only statistically significant predictors with hazard ratios of 1.12 (95% CI [1.00-1.25], p=0.050) and 7.43 (95% CI [1.62-34.0], p=0.010) respectively. While absence of lymphocytes had a trend towards increased hazard ratio (3.44 95% CI [0.98-12.1]) it did not meet the threshold for statistical significance in a univariable model (p=0.054).
To confirm that presence/absence of TILs was an independent prognostic factor for PFS, we generated a multivariable Cox-proportional hazards model using ulceration, tumor thickness, and absence of TILs as predictors (Table 4 ). Ulceration and absence of TILs were the only variables associated with significantly worse PFS. In this model, the hazard ratio for ulceration was 16.1 (95% CI [2.60-99.5], p=0.003). For absence of TILs the hazard ratio was 9.45 (95% CI [1.99-44.8], p=0.005). This indicates that patients with an ulcerated lesion at biopsy had a 16.1x greater risk of disease progression. Patients with absent TILs at biopsy had a 9.5x greater risk of disease progression compared to those with TILs present.