ESTRO 2025 - Abstract Book

S1681

Clinical - Sarcoma & skin cancer & malignant melanoma

ESTRO 2025

Material/Methods: Data of elderly patients (aged ≥ 70years) with histologically proven non-melanoma skin cancer lesion(s) were retrospectively analyzed. All lesions were treated with definitive hypofractionated RT. A decision tree methodology was applied to define significant pre-treatment parameters of cCR rate. The data set contained seven predictor variables referred to each lesion (location, histology, T stage, diameter, bleeding, pain, previous treatment). Continuous covariates were dichotomized and dichotomized variables were normalized to “0” or “1” values. The dependent variable referred to lesion response to RT (cCR or no cCR). The open-source R software was used. Important explanatory variables were selected using the random forest approach. A classification tree that optimally partitioned patients according to cCR was then built. Results: A total of 109 patients (male=59) with 133 non-melanoma skin cancer lesions were included in the analysis. Mean age at diagnosis was 85.7years (range 70-98years) and 30.3% of patients (n=33) were qualified for home health care or lived in a nursing home. Overall, 58 patients (53.2%) referred local pain at diagnosis and bleeding lesion was evident in 52 cases (39.1%). Each lesion received the prescribed hypofractionated RT dose. The top three important predictors were T stage, location and pain with a mean decrease Gini of 5.76, 4.56 and 3.34%, respectively. These covariates were used to grow an optimal classification tree (Figure 1). Overall, the tree had five terminal nodes, which resulted in partitioning non-melanoma skin cancer lesions in five groups: (i) T1-2 lesions (69% of the overall sample, with 91% probability of cCR); (ii) T3-4 lesions without pain (22% of the overall sample, with 72% probability of cCR); (iii) painful T3 lesions located on the ear, pre/retro-auricolar region, or forehead-temples or cheek area (3% of the overall, 75% cCR probability); (iv) painful T4 lesions located on the ear, pre/retro-auricolar region, or forehead temples or cheek area (1% of the overall, 0% cCR probability); (v) painful T3-4 lesions located on the scalp, or nose, or orbital/periorbital/chin/neck area or extremities (5% of the overall, 14% cCR probability).

Figure1. Classification tree

Conclusion: T stage at diagnosis, location and pain were of relative importance to predict cCR in non-melanoma skin cancer treated with definitive hypofractionated RT.

Keywords: non-melanoma skin cancer, skin cancer