ESTRO 2024 - Abstract Book

S1537

Clinical - Lower GI

ESTRO 2024

All stage IV (by AJCC 8th edition) were excluded. Primary endpoints were overall survival(OS), disease-specific survival(DSS) and treatment response rate at 8 weeks post-chemoradiotherapy/radiotherapy evaluated by pelvic MRI. Secondary endpoints were 5-year local recurrence rate; acute and late toxicity rates(by CTCAE v.5). Descriptive and survival statistical analysis was accomplished with Kaplan-Meier, Cox regression and Pearson's chi-squared test.

Results:

Mean age at diagnosis was 63 years and the ratio of women to men was 2.5:1. Overall survival at 1-year was 90.5% and 71.6% for both 3 and 5-years. Disease-specific survival at 1-year was 95% and 75.2% for both 3 and 5-years.

Out of 21 patients, 47.6% were HPV-16 positive, 28.3% were smokers and 9.5% were HIV-positive. Most of the tumours were primarily localized in the perianal region (57%) followed by the anal region(43%).

By staging, IIIC (42.9%) was more prevalent, followed by IIA (28.6%), I (14.3%) and IIIA (14.3%). By histology, non keratinizing squamous-cell-carcinoma(SCC) was 47.6%, keratinizing SCC was only 23.8% while 28.6% of cases were SCC with unreported differentiation. For patients with node-positive(N+) disease at diagnosis, there was 1.86 (0.37-9.28, p=0.450) times risk of fatality than for node-negative(N0) anal cancer. The mean survival time for status N0, at diagnosis, was 70 months while it decreased to 57 months for those with status N+. The 3-year and 5-year OS for node-positive(N+) was 55.9% while the 3-year and 5-year OS for node-negative(N0) remained at 88.9%. The overall complete treatment response rate at 8 weeks post-chemoradiotherapy was 76.2%(Χ 2 The group of patients that underwent chemoradiotherapy (57%) achieved a 70%(Χ 2 6 =1.81, p=0.94) complete response rate; 33% had chemoradiotherapy followed by a boost with HDR-BT(high dose-rate brachytherapy) achieving a 90%(Χ 2 6 =1.81, p=0.94) complete response rate; 4.7% (1 patient) received intensive radiotherapy with complete response; 4.7% (1 patient) received HDR-BT after excisional biopsy also with complete response. 6 =1.81, p=0.94).

All patients treated with EBRT underwent conventional fractionation. Helical-IMRT was the most used technique(52%), followed by 3D-CRT(38%) and VMAT at only 14%.

The 5-year local recurrence rate was 4% and median follow-up was 34 months.

Regarding acute toxicity (by CTCAE v.5), 70%(Χ 2 experienced grade 3-4 acute toxicity while only 30%(Χ 2

10 =10.58, p=0.39) of those treated with conventional 3D-CRT

10 =10.58, p=0.39) of the group treated with IMRT techniques had grade 3. Overall, 66.7% of patients had grade 1-2 radiation dermatitis, 28.6% had grade 3 and 4.8% had grade 4.

For late toxicity (by CTCAE v.5), 85.7% of patients had grade 1 radiation proctitis and only 14.3% had grade 2; 9.5% had grade 1-2 anal stenosis.

There were no discernible differences in acute or late toxicity severity between HIV-positive patients and the HIV negative group.