This study is a multicenter cross-sectional observational study, aiming to include approximately 200 patients aged 18-75 years who are using hydrocodone sustained-release tablets or oxycodone sustained-release tablets for pain management of moderate to severe cancer pain. Baseline information, tumor history, and comorbidities of the subjects will be collected through electronic patient-reported outcomes (ePRO), and the pain condition will be evaluated using BPI, acute pain assessment tools, etc. Sleep-related indicators will be collected using Huawei smart wearable devices and PSQI, ISI scales. Psychological emotional states will be assessed using NCCN psychological distress thermometer, HAMA, HAMD, etc. Blood samples will also be collected for relevant tests. The study sets up a screening baseline assessment period, a 1-week assessment period, and 1-month and 3-month follow-up periods after enrollment. The changes in relevant indicators will be tracked throughout the process, aiming to quantify the association between pain and insomnia, anxiety and depression, and to verify the potential mediating role of sleep disorders between pain and emotional disorders, providing a basis for optimizing the comprehensive symptom management of cancer pain patients.

Inclusion Criteria:

1. Aged 18-75 years.
2. Histopathologically or cytologically confirmed diagnosis of malignancy, with moderate to severe cancer-related pain (NRS ≥ 4 points), meeting the WHO three-step analgesic ladder principle, having received opioid analgesic therapy for at least one week with a stable dose and well-controlled pain.
3. ECOG performance status score ≤ 3.
4. Possess basic cognitive function and ability to complete questionnaire-based assessments and wristband-based sleep monitoring.
5. Voluntarily sign the informed consent form and agree to comply with the study follow-up procedures.

Exclusion Criteria:

1. Severe cognitive impairment, history of psychiatric disorder, or language/communication barriers that precludes completion of the assessments.
2. History of opioid abuse or dependence; history of alcohol or non-opioid substance abuse.
3. Severe hepatic or renal insufficiency (Child-Pugh Class C or eGFR < 30 mL/min).
4. Life expectancy < 3 months.
5. Women of childbearing age without effective contraception, or who are pregnant or breastfeeding.
6. Presence of other serious diseases or special conditions that, in the investigator's judgment, may interfere with the study outcomes.
7. Presence of contraindications to the study drug, such as paralytic ileus, chronic obstructive respiratory disease, or cor pulmonale.

The subjects included patients with moderate to severe cancer pain who meet the inclusion and exclusion criteria for this study.