Pushing the Boundaries of Stereotactic Body Radiation Therapy in Irradiated Territories for Nodal Oligorecurrent Prostate Cancer: Outcomes of the CYGNUS Multicentric Retrospective Study.

PURPOSE: The CYGNUS study aims to assess both toxicity and efficacy of stereotactic body radiation therapy performed as salvage approach for pelvic nodal metachronous oligorecurrent (PNMOR) hormone-sensitive prostate cancer, in previously irradiated territory.

METHODS AND MATERIALS: Inclusion criteria were histologically history of proven prostate cancer, locally treated with a radical intent and a biochemical relapse as defined by the European Association of Urology guidelines. All patients had a radiological suspicion of PNMOR, defined as a recurrence occurring in pelvic nodal areas with up to 5 suspect lymph nodes. Reirradiation was defined according to the European Society for Radiotherapy and Oncology-European Organisation for Research and Treatment of Cancer (ESTRO-EORTC) consensus on reirradiation as an irradiation with a geometric overlap with a previous course of radiation therapy.

RESULTS

A total of 155 reirradiation among 150 patients relapsing on 192 nodal sites were retrospectively included, from 13 French centers. The majority of patients (80.7%) received radical prostatectomy as primary treatment. After a median follow-up of 30.5 months, late grade 2 and grade 3 gastrointestinal and genitourinary toxicity occurred in 1.9%, 0%, and 7.1%, and 2.6% of the cases, respectively. The 2-year radiological progression-free survival reached respectively 44.6% (95% CI, 36.2%-55%). The 2-year androgen deprivation therapy-free survival (ADT-FS) reached 52.6% (95% CI, 42%-65.9%). Previous ADT prescription was predictive in multivariable analysis of both radiological progression-free survival (hazard ratio, 2.02; 95% CI, 1.25-3.26; P = .004) and ADT-FS (hazard ratio, 2.49; 95% CI, 1.28-4.72; P = .006). A prostate-specific antigen doubling time <5 months correlated with a shorter ADT-FS (area under the curve, 0.629; P = .014).

CONCLUSIONS

The CYGNUS retrospective study suggests that reirradiation with stereotactic body radiation therapy for PNMOR is associated with a low rate of toxicity. However, further data with plan summation and longer follow-up are needed to confirm these findings.