Neoadjuvant Chemoradiotherapy Combined With PD-1 Inhibitor and Thymalfasin for Locally Advanced Mid-low Rectal Cancer

Study Purpose

• To evaluate the efficacy and safety of neoadjuvant chemoradiotherapy combined with PD-1 inhibitor and thymalfasin for locally advanced mid-low rectal cancer.
• To explore the effects of neoadjuvant chemoradiotherapy combined with PD-1 inhibitor and thymalfasin on the immune microenvironment of locally advanced mid-low rectal cancer.

Study Design: A single-center, retrospective, controlled study Subjects were divided into two groups according to whether or not they received thymalfasin: group 1 was treated with neoadjuvant chemoradiotherapy combined with PD-1 inhibitor, and group 2 was treated with neoadjuvant chemoradiotherapy combined with PD-1 inhibitor and thymalfasin.

Subjects received long course radiotherapy (50 Gy/25f, 2 Gy/f, 5 days/week) for the first 5 weeks and three 21-day cycles capecitabine (1000 mg/m2, bid, po, day1-14) plus three 21-day cycles tislelizumab (200 mg, iv.gtt, day 8) for the first 9 weeks. After that, patients rested for two weeks (week 10-11)。6-8 weeks after the end of radiotherapy, patients underwent TME surgery (12-14 weeks). Thymalfasin was started on the first day of neoadjuvant chemoradiotherapy, 1.6 mg subcutaneously twice a week until the end of the last neoadjuvant treatment.

Enrollment: preoperative Tα1 (n=14), postoperative Tα1 (n=7), or no Tα1 (n=26) Study Population: locally advanced mid-low rectal cancer Primary Endpoint: 3-y DFS, pCR rate Exploratory endpoint: Paraffin specimens were collected from biopsies before neoadjuvant therapy and after surgery in patients meeting the inclusion criteria. The expression of CD86, CD163, CD4+T，CD8+T，PD-1 were detected.

Inclusion criteria

• Patients with rectal adenocarcinoma must satisfied all the following conditions:

• Stage II/III LARC (cT1-4aN0-2M0);
• Tumor distal location≤10 cm from anal verge (MRI diagnosed);
• Patients regardless of gender with aged≥18 years
• ECOG score of 0 or 1
• Physical and viscera function of patients can withstand major abdominal surgery

Exclusion criteria

• Current or previous active malignancy other than rectal cancer；
• Patients underwent major surgery within 4 weeks prior to neoadjuvant therapy；
• Patients have any condition affects the absorption of capecitabine through gastrointestinal tract；
• Patients have severe uncontrolled recurrent infections, or other severe uncontrolled concomitant diseases;
• Patients with severe concomitant diseases with estimated survival≤5 years；
• Patients with present or previous moderate or severe liver and kidney damage；
• Patients preparing for or previously received organ or bone marrow transplant；
• Patients who have received immunosuppressive or systemic hormone therapy within 1 month prior to the start of neoadjuvant therapy；
• Patients with congenital or acquired immune deficiency (such as HIV infection)；
• Pregnant or lactating women.