The goal of this single center prospective observational study is to determine the effect of chemotherapy on (the change in) vital parameters. The main question it aims to answer are: Can changes in vital parameters be measured by using a Fitbit in patients with cancer while undergoing chemotherapy. Participants will be asked to wear a Fitbit for the first two cycles of chemotherapy to evaluate the changes in vital parameters.

The goal of this single center prospective observational study is to determine the effect of chemotherapy on (the change in) vital parameters. The main question it aims to answer are: Can changes in vital parameters be measured by using a Fitbit in patients with cancer while undergoing chemotherapy. Participants will be asked to wear a Fitbit for the first two cycles of chemotherapy to evaluate the changes in vital parameters. Patients will start measuring in the week prior to the first cycle of chemotherapy, target is at least 4 to 7 days before initiation of chemotherapy. Patients were the Fitbit as much as possible, during day and night. Patients continuously carry the Fitbit during the first 3 months of systemic treatment, which tracks their vital signs. At the starting day of the next cycle of chemotherapy patients will have an appointment with one of the researchers to evaluate the use of the Fitbit. Furthermore, it will be checked if a patient has returned to their baseline vital signs.

Inclusion Criteria:

• Age ≥18 years;
• Diagnosis of stomach or esophageal cancer with an indication of starting chemotherapy
• Knowledge how to handle a Fitbit
• Mastery of Dutch language
• Able and willing to give written informed consent

Exclusion Criteria:

• Cognitive disorders or severe emotional instability
• Already participating in an exercise trial

All patients with stomach and esophageal malignancies referred for chemotherapy of the outpatient clinic at the department of Medical Oncology at the Erasmus University Medical Center.