Interim analysis of a phase II study of simultaneously integrated boost intensity modulated radiation therapy (SIB-IMRT) in combination with 5-FU and mitomycin-C among patients with locally advanced anal canal cancer.

Abstract

e15501 Background: Concomitant radiochemotherapy is the standard treatment of locally advanced epidermoid anal canal carcinoma (EACC) but conventional radiotherapy (RT) frequently induces significant non-hematological toxicities, resulting in long treatment breaks. Given the numerous anatomic pelvic structures, EACC has become of interest for Intensity-Modulated Radiation Therapy (IMRT) despite the induced cutaneous toxicities responsible for RT breaks. Given the deleterious effect of treatment duration on local control and survival in other epidermoid cancers, continuous IMRT is challenging to control EACC. Several SIB-IMRT schedules provided similar results with moderate doses and schedules delivering higher doses with short breaks. Yet, standard SIB-IMRT schedule in EACC still not exists. We propose to concomitantly assess the safety and efficacy of continuous SIB-IMRT without planned breaks and concurrent chemotherapy (CT) to improve the treatment of locally advanced EACC by reducing the proportion of patients (pts) requiring RT breaks for toxicities. Methods: The CANAL-IMRT-01 phase 2 trial (NCT02701088) targets pts with histologically proven EACC candidate for concomitant RT of pelvic and inguinal nodes plus CT. Applying a two-step Bryant & Day design, the main criterion is based on both efficacy and safety. Efficacy is defined as the proportion of pts alive with no local disease progression 3 months after the end of IMRT; safety is defined as the proportion of pts with no RT breaks required by grade ≥3 toxicities. Assuming the unacceptable and acceptable proportions of pts without toxicity requiring IMRT break are 60 and 80% respectively, the unacceptable and acceptable 3-month-progression-free-survival are 80 and 90%, 14 assessable pts at first step and 46 in the second are required (alpha risk 5%, 90% power). To anticipate a 10% drop out rate, 16 pts were needed in first step, with ≥11 objective local responses and ≤6 toxicity-induced IMRT breaks to pursue. Treatment consists in 50 days of concomitant CT (2 cycles of 5FU and Mitomycin-C) and SIB-IMRT delivered by helical tomotherapy: 61.2Gy/1.7Gy to the primary tumor, 57.6Gy/1.6Gy to involved nodes, and 54/1.5Gy to elective pelvic lymph nodes. Results: From December 2015 to June 2017, 16 pts were enrolled: 11 female (73%), median age 62 [55-66]. 15 pts were assessable for efficacy and safety. All 15 pts had a 3-month locoregional response (12 complete responses, 3 partial responses). SIB-IMRT breaks were required by toxicities for 4 out of 15 pts: G1 radiodermitis, G2 inguinal and epithelitis, G1 fever, G3 anorexia and vertigo. Conclusions: The planned interim analysis of continuous SIB-IMRT plus CT allowed pursuing this phase 2 trial to assess the relevance of such schedule for locally advanced ASCC. Enrolment is still ongoing. Clinical trial information: NCT02701088.