Intrinsic radiosensitivity, genomic-based radiation dose and patterns of failure of penile cancer in response to adjuvant radiation therapy

Abstract

Purpose

Optimal postoperative radiation therapy (PORT) dose is unclear in penile squamous cell carcinoma (PeSCC). Herein, we characterized the radiosensitivity index (RSI) and genomic-adjusted radiation dose (GARD) profiles in a cohort of patients with PeSCC, and assessed the application of GARD to personalize PORT.

Methods

A total of 25 PeSCC samples were identified for transcriptomic profiling. The RSI score and GARD were derived for each sample. A cohort of 34 patients was reviewed for clinical correlation.

Results

The median RSI for PeSCC was 0.482 (range 0.215–0.682). The majority (n=21; 84%) of cases were classified as radioresistant. PeSCC GARD ranged from 9.56 to 38.39 (median 18.25), suggesting variable therapeutic effects from PORT. We further determined the optimal GARD-based RT doses to improve locoregional control. We found that therapeutic benefit was only achieved in 52% of PeSCC lesions with PORT of 50Gy, in contrast to 84% benefit from GARD-modeled PORT of 66Gy. In the clinical cohort, the majority of patients presented with pathological N2 or N3 disease (n=31; 91%) and was treated with adjuvant concurrent platinum-based chemoradiotherapy (CRT, n=30; 88%). Fourteen of the 34 patients (41%) had locoregional recurrence (LRR), of which half had LRR within six months of completion of PORT.

Conclusions

The majority of PeSCC are intrinsically radioresistant with a low GARD-based therapeutic effect from PORT dose of 50Gy, consistent with the observed high rate of LRR in the clinical cohort. A GARD-based strategy will allow personalizing PORT dose prescription to individual tumor biology and improve outcomes.