3107 - A Real-World Long-Term Outcome of Intensity-Modulated Radiation Therapy plus Concurrent Chemotherapy in Locally Advanced Anal Squamous Cell Carcinoma

T. Xu¹, Y. Tang¹, J. Shi¹, N. Lu¹, B. Chen², Y. Zhai², H. Fang², S. Qi², S. Wang², W. Zhang¹, H. Jing², Y. Liu¹, Y. Song², Y. LI¹, and J. Jin^1,3; ¹State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College (PUMC), Beijing, China, ²Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, ³?Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China, Shenzhen, China

Purpose/Objective(s): Intensity-Modulated Radiation Therapy (IMRT) might reduce mortality and potentially further improve quality of life in squamous cell carcinoma of anus (SCCA), but there were currently limited relevant long-term results. This single-center study reported 5-years outcomes, late toxicity, and anorectal function on SCCA treated with IMRT-based definitive chemoradiation. Materials/

Methods: Since 1 Jan 2010, consecutive 65 patients with T1-4N0-3M0 SCCA treated with IMRT-based concurrent chemoradiation (CCRT), were retrospectively reviewed at single institution. Treatment outcomes including overall survival (OS), disease-free survival (DFS), anal cancer-specific mortality (ACSM), local-regional failure (LRF), distant metastasis (DM) and colostomy failure (CF), late toxicity and anorectal function were analyzed.
Results: With a median age of 52 years, patients were 70.8% female, 30.8% T3-4 lesions and 46.2% clinically nodes-positive. 39 patients were infected with HPV, all of whom were high-risk HPV types, primarily HPV-16 (64.1%). 76.9% received CCRT as initial treatment for SCCA, while 20.0% had undergone local excision and 3.1% received induction chemotherapy before CCRT. Concurrent chemotherapy was administered mainly using the MMC-based regimen (70.7%), followed by the cisplatinum-based regimen (23.1%). All patients received uninterrupted conventional radiotherapy using IMRT technology. Median dose to treat gross disease and elective nodal regions were 54 Gy (with a BED of 65.7 Gy) and 45 Gy respectively. With median follow-up of 60.7 months, the 5-year OS and DFS rates were 82.4% and 74.6%, respectively, surpassing historical result of 78% and 68% on the MMC arm of RTOG 9811 trial. The 5-years rates of ACSM, LRF, DM and CF were 13.9%, 18.0%, 6.5% and 19.0%, respectively. In both univariate and multivariate analysis, BED > 66 Gy to gross disease significantly correlated with OS (HR 4.33, P=.02), DFS (HR 3.27, P=.02) and CF (HR 5.08, P=.006), while its correlation with LRF was marginal (P=.06). The most common grade 3 late AEs were gastrointestinal (6.2%), genitourinary (6.2%) and skin/subcutaneous (4.6%). The grade 3 gastrointestinal late AEs comprised of 2 diarrhea, 1 rectal stricture, 1 ileus and 1 fecal incontinence. Among 49 patients who were exempted from permanent colostomy, median Wexner score was 0 (range: 0-7) and median Vaizey score was 2 (range: 0-10), indicating acceptable anorectal function. Median LARS score was 0 (range: 0-28) with only 3 patients reported minor LARS.
Conclusion: IMRT-based CCRT produced excellent long-term local control in SCCA with manageable long-term toxicity and desirable anorectal function. BED > 66 Gy to gross tumor was a unfavorable factor for OS, DFS and CF.