3297 - Outcomes of Stage IIA and Stage IIB Seminoma Treated with Definitive Radiation Therapy

Purpose/Objective(s): Patients with Stage IIA/IIB seminoma are managed with chemotherapy or radiation (RT) with emerging data on primary surgery. Data on RT techniques and outcomes including secondary cancers is limited. We analyzed the clinical outcomes of patients treated with RT for stage IIA/IIB seminoma in the modern era.

Materials/Methods: Patients with stage IIA and IIB seminoma treated with RT using a “dog-leg” field from 2000 to 2020 were retrospectively identified. The primary outcome was relapse-free survival (RFS), which was calculated by Kaplan-Meier method and compared with log-rank test. Secondary cancers were tabulated and defined as a new cancer within the RT port.

Results: 51 patients were included with median follow-up of 96 months (IQR 46-137 months). 5-year RFS was 88%. 6 patients (12%) developed progression, all within 4 years of RT and occurring outside the treatment field. Patterns of recurrence of seminoma included 4 mediastinal recurrences, 1 supraclavicular (SCV) recurrence, and 1 pulmonary recurrence. All patients were successfully salvaged with chemotherapy, and one patient also received mediastinal RT. 6 patients (12%) developed a subsequent malignancy (2 colon, 1 bladder, 1 DLBCL, 1 T-cell leukemia, 1 with prostate & pancreas cancer). At last follow-up, 3 patients died of secondary cancers, and 2 died of comorbidities unrelated to seminoma progression. Median age of 3 patients who died of secondary cancers was 63 years (range, 51-64). No patients died of seminoma progression. Median time from the start of RT to the development of secondary cancer was 78 months. All secondary cancers occurred in patients treated with 3D conformal RT. Comparing patients who presented with stage IIA/IIB at initial diagnosis (de novo) vs those with stage I seminoma who then developed stage II (relapsed), no difference was observed in RFS (HR 0.99, 95% CI, 0.2-5.4, p=0.99). 19 patients (37%) received prophylactic left SCV RT. No difference was observed in RFS between prophylactic SCV RT and no SCV RT (HR 0.84, 95% CI 0.2-4.6, p=0.84). 34 patients (67%) experienced acute grade 2 GI toxicity during RT, most commonly nausea. There were no grade 3+ toxicities observed. On univariate analysis, there was no association of RFS with lymph node size, node number, age at diagnosis, or LVI on orchiectomy pathology.

Conclusion: Stage IIA and IIB seminoma patients have exceptional RFS and OS with RT. All patients with progressive disease were salvaged effectively. Secondary malignancies occurred only in patients treated with 3D conformal technique and none occurred after IMRT or proton RT, thus suggesting judicious use of 3D conformal technique.