Patients with incurable gastroesophageal cancer are at high risk of cancer cachexia with an estimated prevalence of 60-80%. Cancer cachexia is defined as ongoing loss of skeletal muscle mass with or without loss of fat mass and is associated with impaired quality of life, loss of physical function, treatment intolerability, and increased mortality.

Cancer cachexia is a multifactorial syndrome, and in patients with gastroesophageal cancer, the wasting is compounded by a high prevalence of dysphagia. To date, no drug therapy has been approved for the treatment for cancer cachexia. Sufficient nutritional support is imperative in cachexia treatment, but to effectively treat cancer cachexia there is a need to fully understand the biological mechanisms underpinning the wasting syndrome.

The primary objective of the present cohort study is to determine the incidence and extend of skeletal muscle wasting in patients with incurable gastroesophageal cancer. The investigators will also investigate the prevalence of low skeletal muscle at time of diagnosis. The secondary objective is to investigate, if loss of skeletal muscle is associated with treatment intolerance and increased mortality.

Furthermore, the investigators aim to explore factors differentially expressed in the circulation, in skeletal muscle, and in adipose tissue of patients experiencing wasting compared with patients not experiencing wasting.

The study is a prospective cohort study including patients with incurable gastroesophageal cancer referred to first line chemotherapy. Blood and plasma samples as well as clinical and simple functional assessments will be obtained from all patients. The participants will also be offered to take part in a sub-study in which, we will collect skeletal muscle and subcutaneous adipose tissue.

The main questions the investigators aim to answer are:

• What is the prevalence and extent of skeletal muscle mass wasting in patients with incurable gastroesophageal cancer?
• Are the loss of skeletal muscle mass and low skeletal muscle mass associated with treatment intolerability and overall survival in patients with incurable gastroesophageal cancer?
• Can there be identified potential biological processes and factors in skeletal muscle, adipose tissue, and plasma that contribute to the loss of skeletal muscle mass in patients with incurable gastroesophageal cancer?

Inclusion Criteria:

• Patients eligible for participation are any patient diagnosed with histologically verified, incurable cancer of the esophagus, stomach, or gastroesophageal junction, referred to first line chemotherapy.

Exclusion Criteria:

• Age < 18 years

Patients diagnosed with histologically verified, incurable cancer of the esophagus, stomach, or gastroesophageal junction, referred to first line chemotherapy.