This study aims to evaluate the safety and efficacy of 3D1002 alone or in combination with oxycodone hydrochloride sustained-release tablets (OxyContin) for the management of moderate or severe cancer pain.

The investigational product in this study, 3D1002, is a selective antagonist of prostaglandin E2 receptor subtype 4 (EP4). The study is composed of two stages. Phase IIa stage is to assess the safety and efficacy of 3D1002 administered at doses of 50, 100 or 150 mg every 12 hour (q12h) for patients with moderate to severe cancer pain, and to determine the optimal recommended dose for further studies. Phase IIb stage is to evaluate the difference in the efficacy and safety of 3D1002 combined with OxyContin and OxyContin alone in treatment of patients with moderate to severe cancer pain.

Inclusion Criteria:

1. Subject must sign the informed consent in person prior to beginning any screening procedure.
2. Age ≥18, both male and female.
3. Subjects with a malignant tumor confirmed by histopathology or cytology.
4. Weight ≥40 kg at screening period.
5. Subjects have relatively stable cancer pain and require continuous analgesic medications (estimated treatment duration ≥2 weeks), as assessed by the investigator.
6. Estimated life expectancy ≥3 months.
7. Subjects are willing to not use any analgesic other than those specified in the study during the study treatment period.
8. ECOG PS score is 0-3.
9. Have adequate organ and bone marrow function.
10. The mean NRS scores per day during the washout period are ≥4.

Exclusion Criteria:

1. Known allergy to any of the active ingredients or excipients of the study drug, or have a history of allergy to other opioids or non-steroidal anti-inflammatory drugs (NSAIDs) and their related ingredients.
2. Have a persistent pain resulted from other medical conditions or unknown causes.
3. Subjects presenting with emergency symptoms such as intestinal obstruction/perforation, spinal cord compression, epidural metastasis, or fracture.
4. Subjects with known active/symptomatic central nervous system metastasis and/or cancerous meningitis.
5. Subjects plan to be treated with >10 mg/ day of prednisone or equivalent systemic corticosteroid during the study period.
6. Have a history of gastrointestinal bleeding or perforation.
7. Have a positive result of fecal occult blood test during screening period.
8. Have a history of serious cardiovascular diseases.
9. Have a history of an acute ischemic or hemorrhagic stroke within 6 months prior to screening.
10. Have a history of significant psychiatric disorders, such as schizophrenia and depression.
11. Subjects plan to receive radiotherapy, surgery, or a new regimen of systemic antitumor agents during the study treatment period (D1-D15).
12. Subjects have a history of alcohol abuse or drug abuse including opioids.
13. Subjects have significant opioid contraindications.
14. Pregnant or lactating women.
15. Subjects with other diseases that affect the oral administration or absorption of drugs.
16. Subjects are currently participating in another clinical study.
17. Other conditions deemed by the investigator to be inappropriate for participation in this study, such as poor compliance.