Imaging-related irradiation can safely be reduced in patients with stage 1 seminoma following orchiectomy
Computerised tomography (CT) surveillance has become the standard-of-care following orchiectomy of a stage 1 seminoma. Patients with stage 1 seminoma are typically younger and avoiding unnecessary radiation is crucial to the avoidance of a secondary malignancy. In this respect, results of the phase III TRISST study demonstrate the non-inferiority of a reduced, 3-scan MRI surveillance protocol, compared to a typical 7-scan CT protocol.
Introduction
Stage 1 seminoma is the most common presentation of testicular cancer and it is associated with a survival rate of almost 100% following orchiectomy. Computerised tomography (CT) surveillance has become the international standard-of-care, replacing adjuvant treatment strategies in these typically young patients. However, avoiding unnecessary radiation is essential to ensuring secondary malignancies do not occur. Furthermore, the optimal frequency or modality of scans is currently undefined in literature. In this light, the phase III TRISST study aimed to safely reduce the number of CT scans in a typical surveillance protocol or replace them with magnetic resonance imaging (MRI) scans.
In the TRISST trial (1:1:1:1) 669 men with confirmed stage I seminoma, who had subsequently undergone an orchiectomy were randomly assigned to receive a total of 7 CT or MRI scans (6, 12, 18, 24, 36, 48, 60 months) or a reduced protocol of 3 CT or MRI scans (6, 18 and 36 months). The primary outcome of the trial consisted of 6-year incidence of RMH ≥stage IIC relapse (≥5 cm). Key secondary objectives included the rate of ≥3 cm relapses, overall survival (OS) and disease-free survival (DFS).
Imaging frequency can safely be reduced
The mean age of participants in this study was approximately 39 years. Across the 4 cohorts (7 CT, 3 CT, 7 MRI and 3 MRI), the mean maximum tumour diameter was 2.9 cm, with 20% having a tumour >4 cm. Approximately 13% of patients had > T grade 1 disease. At a median follow-up of 72 months, 12% of patients (N= 82) had relapsed, with a slightly higher incidence in the the 3-scan cohorts compared to the 7-scan cohorts. Importantly, however, difference this was found to be statistically non-inferior. Overall, 4 of the 9 stage ≥IIC relapses in the 3-scan cohorts were thought to have been identifiable earlier, had these patients been in the 7-scan cohorts. In the intention-to-treat analysis, the 6-year incidence of ≥ stage IIC relapse with 3- and 7-scans was 2.8% vs. 0.3% respectively, with the incidence of relapse ≥3cm following a similar trend (4.7% vs. 2.7%). In relation to the primary outcome, fewer events occurred with MRI compared to CT (0.6% vs. 2.6%), with the incidence of relapse ≥3 cm occurring at a rate of 3.4% vs. 4.1%, respectively. Generally, very few (<1%) relapses occurred after 3 years. Post-progression treatment typically consisted of chemo/radiotherapy, with 81% of patients achieving a complete response. 5-year DFS was 87%, with an OS of 99% and no deaths during this follow-up period.
Conclusion
This study found MRI scans to be non-inferior to CT, and also showed that a 3-scan surveillance protocol is non-inferior to the standard 7-scan protocol. With this 3-scan protocol, a total of 1,017 scans were avoided. This came at the cost of 4 avoidable stage ≥IIC relapses. These findings, combined with the favourable long term survival outcomes for patients with stage I seminoma after an orchiectomy, lead to the conclusion that a reduced 3-scan MRI surveillance protocol is a viable alternative to current CT practises.
Reference
Joffe JK et al., Imaging modality and frequency in surveillance of stage I seminoma testicular cancer: Results from a randomized, phase III, factorial trial (TRISST). Presented at ASCO GU 2021; Abstract 374.
