Inclusion Criteria:  Patient whose age ≥ 18 years Patient with locally advanced squamous cell carcinoma of the anal canal for which he/she has received radiotherapy/chemotherapy: tumor > 2cm and/or locoregional lymph node involvement Patient whose main treatment (radiotherapy and chemotherapy) was performed at the Paris Saint-Joseph Hospital French-speaking patient  Exclusion Criteria:  Patient with missing or unanalyzable material Patient with missing data Patient under guardianship or curatorship Patient deprived of liberty Patient under court protection Patient objecting to the use of his data for this research