This is a single-center, open-label, single-arm clinical study aimed at conducting a preliminary evaluation of the efficacy and safety of combining PCSK9 inhibitors and PD-1 inhibitors (dual inhibitors) with neoadjuvant chemoradiotherapy in patients with pMMR/MSS locally advanced rectal cancer.

This study aims to evaluate the complete response (CR) rate of PCSK9 inhibitor and PD-1 inhibitor combination therapy (dual inhibitors) in conjunction with neoadjuvant chemoradiotherapy for patients with pMMR/MSS locally advanced rectal cancer. Specifically, the study will assess the pathological complete response (pCR) rate two weeks after neoadjuvant therapy, the clinical complete response (cCR) rate under the "watch-and-wait" strategy, objective response rate (ORR), R0 resection rate, tumor regression grade (TRG), and sphincter preservation rate. Additionally, the study will evaluate the 2-year disease-free survival (DFS) and overall survival (OS) following dual-inhibitor combined neoadjuvant chemoradiotherapy. The safety and tolerability of this combination therapy will also be comprehensively assessed based on NCI-CTCAE 4.03 criteria.

Inclusion Criteria:

1. Age between 18 and 75 years, regardless of gender;
2. Histologically confirmed pMMR/MSS rectal adenocarcinoma, with clinical staging of cT3/T4 or cN+, and tumor located ≤12 cm from the anal verge;
3. No distant metastasis;
4. ECOG performance status of 0-1;
5. Baseline hematological and biochemical parameters meet the following criteria: neutrophils ≥1.5×10^9/L, hemoglobin ≥90 g/L, platelets ≥100×10^9/L, ALT/AST ≤2.5 ULN, creatinine ≤1 ULN;
6. Good compliance and willingness to sign an informed consent form.

Exclusion Criteria:

1. History of allergies to PCSK9 monoclonal antibody, PD-1 monoclonal antibody, capecitabine, or oxaliplatin;
2. Preoperative pathological diagnosis of non-pMMR/MSS rectal adenocarcinoma;
3. Use of other long-term lipid-lowering drugs leading to conditions such as hypolipidemia;
4. Pregnant or breastfeeding women;
5. History of other malignancies within the past 5 years;
6. Previous history of anti-tumor treatments, including radiotherapy, chemotherapy, immune checkpoint inhibitors, T-cell related therapies, etc.;
7. History of severe neurological or psychiatric disorders (e.g., schizophrenia, dementia, or epilepsy);
8. Current severe cardiovascular disease (heart failure or arrhythmia), renal insufficiency, or liver dysfunction; Note: Whether the patient can tolerate the specific treatment or measures should be assessed by a cardiologist based on the patient's condition.
9. Acute myocardial infarction or ischemic stroke within 6 months prior to enrollment;
10. Presence of uncontrolled infections requiring systemic treatment;
11. Active autoimmune diseases or immunodeficiencies, a history of organ transplantation, or systemic use of immunosuppressive agents;
12. Known history of HIV infection (e.g., HIV 1-2 antibody positive), active syphilis, or active pulmonary tuberculosis;
13. Active hepatitis B virus (HBV) or hepatitis C virus (HCV) infection during screening (e.g., HBsAg positive, HBV DNA positive, HCV RNA positive, or anti-HCV antibody positive);
14. Known allergy to any component of the treatment;
15. Investigator's judgment that other factors exist which may cause early termination of the trial, such as severe disease (including psychiatric disorders), alcohol abuse, drug use, or social or familial factors affecting patient safety or compliance;
16. History of hypocholesterolemia (total cholesterol [TC] <3.6 mmol/L or <140 mg/dL, low-density lipoprotein cholesterol [LDL-C] <1.8 mmol/L or <70 mg/dL, high-density lipoprotein cholesterol [HDL-C] <1.0 mmol/L [male] or <1.3 mmol/L [female]), hypolipidemia (triglycerides [TG] <0.5 mmol/L or <45 mg/dL), or a family history of these conditions.