This clinical trial aims to evaluate the efficacy and safety of acupoint application with Gutong Plaster for treating moderate to severe cancer pain in patients aged ≥18 years with moderate to severe cancer pain (NRS 4-8), ECOG 0-3, life expectancy ≥3 months. The main questions it aims to answer are:

Does acupoint application with Gutong Plaster improve the response rate (CR + PR) in patients with moderate to severe cancer pain? Does Gutong Plaster reduce pain intensity (NRS score) and opioid consumption in cancer pain patients? Researchers will compare patients receiving oxycodone plus Gutong Plaster to patients receiving oxycodone plus placebo simulant to see if Gutong Plaster provides better pain relief and lower opioid use.

Participants will:

Receive standard treatment with oxycodone prolonged-release tablets Be randomly assigned to receive Gutong Plaster or placebo simulant via acupoint application twice daily for 14 days Undergo pain assessment, quality of life evaluation, safety laboratory tests, and follow-up at specified time points

Inclusion Criteria:

1. The subject has signed the informed consent form.
2. Age ≥ 18 years, including males and females.
3. According to the investigator's assessment, the subject has relatively stable cancer pain and requires continuous analgesic medication (estimated treatment duration ≥ 2 weeks).
4. Estimated life expectancy ≥ 3 months.
5. Eastern Cooperative Oncology Group (ECOG) performance status score of 0-3.
6. Adequate organ function.
7. Patients with moderate to severe cancer pain, defined as 4 ≤ NRS (Numeric Rating Scale) score ≤ 8.

Exclusion Criteria:

1. Known allergy to any active ingredient or excipient of the study drug, or a history of allergy to other opioids and their related components.
2. Persistent pain caused by other diseases or unknown causes.
3. Subjects presenting with urgent symptoms such as intestinal obstruction/perforation, spinal cord compression, or pathological fracture.
4. History of severe psychiatric disorders, such as schizophrenia and depression.
5. Patients currently receiving chemotherapy or still in the chemotherapy reaction period (patients in the chemotherapy interval may be included. That is, patients who have completed chemotherapy for more than 1 week can be enrolled, or patients who have just finished chemotherapy may be enrolled at the investigator's discretion).
6. Patients who have received radiotherapy to the pain area within 4 weeks before enrollment (those who have received radiotherapy to areas other than the pain area may be included), or those who plan to receive radiotherapy to the pain area during the study.
7. Other conditions deemed unsuitable for participation in this study by the investigator, such as poor compliance.