Over the past 20 years, China's obesity rates have surged, increasing cancer burden. Obesity links to 13 cancers via metabolic effects of visceral fat and insulin resistance, while sarcopenic obesity (BMI-independent) may worsen outcomes. Traditional BMI lacks precision; advanced methods (e.g., BIA/CT) are needed. Existing studies show inconsistent results, possibly due to heterogeneity. This multicenter prospective cohort study uses imaging to assess body composition changes (fat/muscle) in obesity-related tumors and their impact on survival, recurrence, and quality of life, and explore the underlying mechanism.

Inclusion Criteria:

1. Age ≥18 years, regardless of gender.
2. Histologically or cytologically confirmed obesity-associated malignant tumors (e.g., breast cancer, colorectal cancer, gastric cancer, lung cancer, or thyroid cancer) with planned treatment after diagnosis (any treatment modality permitted).
3. No prior chemotherapy, radiotherapy, biologic therapy, immunotherapy, or other antitumor treatments for malignancy.

Exclusion Criteria:

1. Patients with concurrent non-obesity-related malignancies.
2. History of prior malignancy (except completely cured carcinoma in situ of the cervix, basal cell carcinoma, or squamous cell carcinoma of the skin).
3. Patients with concurrent multiorgan dysfunction syndrome, autoimmune diseases, infectious diseases, neurological disorders, or psychiatric disorders.

Study participants will be enrolled if they are under clinical care in oncology-related departments