With increasing age and the additional impact from the bowel cancer and the chemotherapy and/ or radiotherapy it has been described that testosterone (a male hormone produced naturally in the body) levels are reduced. Testosterone has an impact on numerous body functions including the muscle mass and quality. Previous studies have identified that muscle mass is reduced as a result of ageing but also because of the deleterious effect of cancer and chemotherapy and/or radiotherapy. There is growing evidence from published studies that patients with better muscle mass and quality, do better after surgery. Mr Jenkins and his team are therefore looking at ways, the investigators can try and prevent or reduce this muscle loss and therefore improve patient outcomes.

The aim of this study is to assess whether using testosterone replacement therapy in the form of a topically applied gel daily for a total of 12 weeks, is feasible and acceptable by the patients who are diagnosed with colorectal cancer and are waiting to undergo surgery. The investigators will also collect information related to the testosterone replacement therapy such as questionnaires on the quality of life, fatigue and muscle mass, and blood biomarker changes in the blood.

Inclusion Criteria:

• Male ≥ 45 years old
• Colorectal cancer - histology confirmed
• Identified as sarcopenic on latest computerised tomography (CT) scan prior to intervention (part of initial investigations - using Martin et al (2013) criteria - 43cm2/m2 for Body Mass Index (BMI) <25, 53cm2/m2 for BMI>25)
• Documented low or normal testosterone at time of recruitment (<12 nano moles/ Litre (nmol/L)
• Eligible for operative intervention
• Capacity to consent
• Able to mobilise & able to complete the 6 Minute Walk Test (MWT)
• Post completion of chemotherapy/ chemoradiotherapy treatment (if the patient has neoadjuvant treatment)
• Booked straight for surgery with an interim of 4-8 weeks.
• Participation in another concurrent trial/ study is accepted, following discussion between the two trial /study teams

Exclusion Criteria:

• Not sarcopenic on computerised tomography (CT)
• Not eligible for surgery
• History of Deep Vein Thrombosis (DVT)/ Pulmonary Embolism (PE)/ prostate cancer/ breast cancer
• Prostate nodule identified during digital rectal examination (DRE) or magnetic resonance imaging (MRI) pelvis
• Multiple distant metastasis which are non-operable
• Prostate specific antigen (PSA) > 3 nanogram/ mililitre (ng/ml)
• Haematocrit (HCT) >52%
• Severe lower urinary tract symptoms
• Class III/ IV heart failure
• Myocardial Infarct or stroke within the last 6 months
• Dementia / No capacity to consent
• Patient on medications with anti-androgen effect eg spironolactone
• Patients with untreated severe obstructive sleep apnoea
• Morbid obesity as defined by Body Mass Index (BMI) >40
• Uncontrolled hypertension
• Patients on long term steroids during the trial period
• Patient on other anabolic agents
• Not already on treatment for primary hypogonadism
• Patients with bone metastasis

Patients diagnosed with colorectal cancer who attend to the surgical clinic, following completion of their neoadjuvant chemoradiotherapy or for initial review by the surgical team in order to proceed with surgery.