Inclusion Criteria:
* Participants must meet all of the following criteria:
1. Voluntarily sign the written informed consent form prior to the initiation of any study-specific procedures;
2. Age between 18 and 70 years, male or female;
3. Eastern Cooperative Oncology Group (ECOG) performance status score of 0-1, and able to tolerate PET/MR and SPECT/CT examinations;
4. Histopathologically, cytologically, or clinically confirmed diagnosis of sarcoma, with at least one measurable lesion according to RECIST 1.1 criteria;
5. At least one measurable lesion with SUVmax ≥ 3.5 on \[68Ga\]Ga-HX01 PET/MR imaging (eligibility to be determined by the investigator, and may be adjusted based on subsequent \[177Lu\]Lu-HX02 SPECT/CT imaging findings);
6. Life expectancy ≥ 6 months;
7. Female participants of childbearing potential must have a negative pregnancy test, and all participants (both male and female) must agree to use effective contraception during the study and for at least 3 months after administration.
Exclusion Criteria:
* Participants who meet any of the following criteria will be excluded from the study:
1. Women who are pregnant or breastfeeding, or who plan to become pregnant during the study or within 3 months after administration \[excluding those who have been postmenopausal for at least 1 year, or who have undergone surgical sterilization (e.g., bilateral tubal ligation without reversal, bilateral oophorectomy, or hysterectomy)\]; or participants (both male and female) who plan to donate sperm or ova during the study or within 3 months after administration;
2. Known or suspected allergy to the investigational product or any of its components, or severe allergic constitution;
3. Have received any treatment within 6 months prior to screening that, in the investigator's judgment, may affect drug absorption, distribution, metabolism, or excretion;
4. Positive syphilis or HIV test at screening;
5. Significant hepatic or renal dysfunction, defined as: serum total bilirubin (TBIL) \> 31.5 μmol/L; aspartate aminotransferase (AST) or alanine aminotransferase (ALT) \> 120 U/L, or \> 200 U/L if the elevation is considered to be related to hepatic metastases from solid tumors; serum creatinine (Scr) \> 150 μmol/L, or creatinine clearance \< 60 mL/min (calculated by the Cockcroft-Gault formula);
6. Abnormal bone marrow function, defined as: absolute neutrophil count (ANC) \< 1.5 × 109/L; hemoglobin \< 10 g/dL; serum albumin \< 2.8 g/dL (normal range: 3.5-5.5 g/dL); platelet count \< 100 × 10⁹/L (normal range: 100-300 × 109/L); international normalized ratio (INR) \> 1.5 (normal range: 0.8-1.3) in patients not receiving warfarin; prothrombin time (PT) \> 2 × ULN (normal range: 11-15 seconds);
7. Presence of active infection (e.g., acute bacterial infection, tuberculosis, active hepatitis B/C, active syphilis, etc.). Active hepatitis B is defined as: positive HBsAg or HBcAb test with HBV DNA titer \> 2500 copies/mL or 500 IU/mL. Active hepatitis C is defined as: positive hepatitis C antibody with detectable HCV-RNA;
8. Difficulty in urination or urinary incontinence due to any cause;
9. Claustrophobia or any other condition that prevents the subject from undergoing PET/MR and SPECT/CT examinations;
10. Psychiatric disorders, such as depressive symptoms, schizophrenia, delusions, hallucinations, or suicidal ideation;
11. Severe cardiovascular disease, including but not limited to New York Heart Association (NYHA) class II-IV congestive heart failure or left ventricular ejection fraction (LVEF) \< 50% or below the lower limit of normal;
12. Any other condition that, in the investigator's opinion, makes the participant unsuitable for participation in this study.
