Long-Course Concurrent Chemoradiotherapy With Adebrelimab and Apatinib as Neoadjuvant Therapy for Locally Advanced/Low-Lying Rectal Cancer Requiring Sphincter Preservation

Inclusion Criteria:

1. Age: 18 to 75 years, male or female;
2. Histologically or cytologically confirmed rectal cancer with measurable tumor lesion(s) (spiral CT or MRI scan ≥10 mm, meeting RECIST 1.1 criteria);
3. Clinical stage: rectal cancer cT3-4N0M0 or cT1-4N+M0, and low rectal cancer with a sphincter-preservation requirement (distance from the anal verge \<5 cm; stage T2N0M0);
4. Expected survival \>3 months;
5. ECOG PS score: 0-1;
6. No peritoneal metastasis or other distant metastasis;
7. No prior radiotherapy or immune checkpoint inhibitor therapy for rectal cancer;
8. Adequate function of vital organs as required (without the use of any blood components or cell growth factors during screening):

   Absolute neutrophil count ≥1.5×10⁹/L; platelet count ≥80×10⁹/L; hemoglobin ≥8.5 g/dL; Thyroid-stimulating hormone (TSH) ≤1×ULN (if abnormal, T3 and T4 levels should also be assessed; patients with normal T3 and T4 levels may be enrolled); Bilirubin ≤1.5×ULN; ALT and AST ≤2.5×ULN; Serum creatinine ≤1.5×ULN;
9. Women of childbearing potential must have a negative pregnancy test (β-HCG) before starting treatment. Women of childbearing potential and men (who are sexually active with women of childbearing potential) must agree to use effective contraception consistently during treatment and for 6 months after the last dose;
10. Subjects voluntarily participate in the study and sign the informed consent form.

Exclusion Criteria:

1. Prior pelvic or abdominal radiotherapy;
2. Tumor expected to be unresectable after neoadjuvant therapy;
3. Pregnant or breastfeeding women, or women/ men of childbearing potential who refuse to use contraceptive measures;
4. History of other malignancies within the past 5 years, except for adequately treated cervical carcinoma in situ or cutaneous squamous cell carcinoma, or well-controlled basal cell carcinoma of the skin;
5. Uncontrolled symptomatic brain metastases, or poorly controlled psychiatric disorders, or severe intellectual or cognitive impairment;
6. Pulmonary fibrosis, interstitial pneumonia, pneumoconiosis, radiation pneumonitis, drug-related pneumonitis, or severely impaired pulmonary function;
7. Active, known, or suspected autoimmune disease. Subjects with stable conditions not requiring systemic immunosuppressive therapy are eligible, e.g., type 1 diabetes, hypothyroidism requiring hormone replacement therapy, and skin conditions not requiring systemic treatment (e.g., vitiligo, psoriasis, and alopecia);
8. Congestive heart failure, uncontrolled arrhythmia, myocardial infarction within 6 months, unstable angina, stroke or transient ischemic attack, severe hypertension refractory to medication, or other conditions rendering the patient unable to tolerate surgery;
9. Severe active infection requiring intravenous antibiotic therapy during the screening period;
10. Known allergy to the study drug or any of its excipients, or a history of severe allergic reaction to other monoclonal antibodies;
11. Clinically significant bleeding symptoms or a clear bleeding tendency within 3 months prior to enrollment;
12. Hypertension that remains uncontrolled despite antihypertensive therapy prior to enrollment;
13. Patients with dysphagia;
14. Receipt of or planned receipt of live vaccines within 30 days prior to administration of adebrelimab;
15. Known history of HIV infection, or active hepatitis B or hepatitis C;
16. Inability to comply with the study protocol or to cooperate with follow-up;
17. Other conditions that the investigator considers inappropriate for participation in this trial.