<qa>  What is the last date of adjuvant therapy?2. Patients must have histologically confirmed esophageal squamous cell carcinoma without prior treatments including surgery, chemotherapy, radiotherapy, and targeting treatment. Patients were allowed to have palliative radiotherapy 3 months before the enrollment and the target lesions should not be within the radiotherapy region. The last date of adjuvant therapy should be over 6 months before the enrollment. 