Radiotherapy for anal squamous cell carcinoma: must the upper pelvic nodes and the inguinal nodes be treated?

BACKGROUND: Loco-regional failure is the predominant cause of death in anal squamous cell carcinoma. We assessed patterns of loco-regional recurrence to determine the impact of radiotherapy (RT) volumes on patient outcome. METHODS: Retrospective clinical study, including patients treated curatively with RT or chemo-radiotherapy between 1994 and 2007. RT fields/volumes were reviewed and compared with patterns of failure. Patients were classified as having whole pelvic radiotherapy (WPRT) if RT extended to L5/S1 or lower pelvic radiotherapy (LPRT) if it extended to the lower sacroiliac joints or below. Patients with negative inguinal nodes either underwent prophylactic inguinal radiotherapy (PIRT) or had inguinal observation (IO). Patterns of failure were compared. RESULTS: Twenty-seven patients (53%) had WPRT and 24 (47%) had LPRT. Forty-two patients had negative inguinal nodes: 29 (69%) had PIRT and 13 (31%) had IO. Median follow-up was 5.8 years. Twelve regional failures occurred in eight patients: three pelvic, one inguinal and four pelvic and inguinal. All patients with regional failure died of disease. Pelvic nodal failure was 7.7% in N0 and 33% in N1-3 patients (P = 0.012). There was no difference in pelvic regional failure between WPRT and LPRT (11% versus 16%, P = 0.64). There was only one possible regional failure above LPRT in this group (4%). Inguinal failure was 0% in the PIRT group compared with 23% in IO group (P = 0.009). CONCLUSION: There was no difference in pelvic regional failure between WPRT and LPRT. LPRT is likely to be safe in N0 patients. Inguinal nodes should be treated in all patients.