This study aims to define the contribution of cancer and chemotherapy to muscle and systemic alterations that drive the onset of cachexia in rectal cancer patients and validate in human cancer cachexia (CC) the alterations in mitochondrial function and neuromuscular junction (NMJ) observed in the experimental models, thus providing the rationale for potential anti-cachexia strategies based on exercise and or exercise mimetics.

This is a multicenter observational prospective cohort study in rectal cancer patients after neoadjuvant therapy (ycTNM) stage II, III, and IV (AJCC 8th edit), clinically stratified in the pre-cachectic or cachectic stage according to Fearon K et al. definition. That will be subject to curative or palliative surgery through any surgical approach. And a control subgroup of patients who will undergo any abdominal surgery type through any approach type for no neoplastic or inflammatory disease.

The study will take place in four Italian centers of colorectal surgery.

Will be run a preoperatory physical performance, and will be recorded the physical activity by wearing a SmartWatch.

The quantity of muscle will be estimated by the cross-sectional area (CSA) or the skeletal muscle area (SMA) from the magnetic resonance imaging (MRI) or computed tomography CT, respectively, and the Skeletal muscle index (SMI). The muscular quality will be studied by the mean skeletal muscle radiation attenuation (SMRA) and MRI proton density fat fraction (PDFF). All these parameters will be calculated by a radiologist from the preoperative MRI or CT imaging study.

The study includes the analysis of preoperatory inflammatory and nutritional biomarkers. And a muscular biopsy harvested by the surgeon from the rectum or oblique abdominal during rectal resection-palliative surgery. The sample will undergo morphological and structural studies using histology, immunohistochemical, immunofluorescence, biochemical, and molecular analyses.

Inclusion Criteria:

• Patients with confirmed histopathological diagnosis of rectal adenocarcinoma ycTNM stage II, III, or IV (AJCC 8th).
• Patients treated with neoadjuvant therapy.
• Patients that will be subject to curative intent or palliative surgery through any approach (open, laparoscopic, or robotic).
• Ability to sign the informed consent.

Exclusion Criteria:

• Rectal cancer stage I or any stage without neoadjuvant therapy.
• Age < 18 and >75 years
• Long steroid treatment for any cause.
• Emergency setting.
• Co-existent inflammatory bowel disease.
• Inflammatory comorbidities (liver failure, diabetes, metabolic acidosis, acute and chronic renal failure, sepsis, AIDS, acute and chronic hepatitis, autoimmune disorders, and chronic obstructive pulmonary disease).
• Healthy volunteers.
• Other (simultaneous) neoplastic disease

Patients from all participating centers older than 18 years, males or females, with the primary diagnosis of rectal cancer ycTNM stage II, III or IV (American Joint Committee on Cancer 8th edition), who undergone neoadjuvant therapy. Clinically stratified in the pre-cachectic or cachectic stage according to Fearon K et al. definition. That will be subject to low or ultralow anterior resection, abdominoperineal resection or palliative surgery through any approach (open, laparoscopic or robotic).