The goal of this study is to improve the monitoring of fluid retention in cancer patients. The main question it aims to answer is: Can segmental bioelectrical impedance analysis be used to monitor local fluid retention (edema) in cancer patients? We will include:

• Breast cancer patients with fluid and or lymph retention in one or both arms after radiotherapy (outpatients)
• Cancer patients with fluid retention in one or both legs after chemotherapy (hospitalized)

Participants will:

• Have measurements taken using bioelectrical impedance
• Provide blood samples and 24-hour urine collection
• Weight monitorering
• Complete diet and fluid registration (inclusive enteral and parenteral)
• Have clinical palpatory and measurement assessment of oedema.

Both groups will undergo measurements over a maximum period of six days.

Outpatients:

Outpatients will complete three measurement cycles, each consisting of two consecutive days:

• Day 1: Home-based dietary and fluid intake registration and 24-h urine collection
• Day 2: Hospital-based assessment including bioelectrical impedance analysis (BIA), blood sampling, body weight measurement, and clinical palpatory assessment

Each measurement cycle will be separated by a 7-14-day interval.

Hospitalized patients:

Hospitalized patients will undergo up to six consecutive measurement days, or until discharge or transfer to another ward:

• Days 1, 3, and 5: Dietary and fluid intake registration and 24-h urine collection
• Days 2, 4, and 6: Bioelectrical impedance analysis (BIA), blood sampling, body weight measurement, and clinical palpatory assessment

If the treating physician administers i.v. loop diuretics to the hospitalized patient, additional measurements will be taken before administration and hourly for five hours thereafter, as these may significantly affect fluid levels.

Inclusion Criteria (Outpatient breast cancer patients with lymphoedema after radiotherapy):

• Habile
• Must be able to speak and read Danish
• Has received/is receiving radiotherapy due to breast cancer within the last 6 months
• Is being followed in the Oncology Outpatient Clinic at Aalborg University Hospital
• Age ≥ 18 years
• Visible lymphoedema in at least one upper extremity

Inclusion Criteria (Hospitalized cancer patients with peripheral oedema in one or both lower extremities after chemotherapy):

• Habile
• Must be able to speak and read Danish
• Has received/is receiving chemotherapy due to cancer within the last 2 months
• Hospitalised in the Oncology Ward at Aalborg University Hospital
• Estimated length of hospital stay of at least 6 days
• Age ≥ 18 years
• Visible peripheral oedema in at least one lower extremity

Exclusion Criteria (both groups):

• Pregnant or breastfeeding women
• Amputated limb(s)
• Pacemaker or implanted cardioverter-defibrillator due to risk of interference from the electrical signal
• Metallic prostheses due to risk of interference with the device signal
• Inability to lie still for the duration of the measurement interval (minimum 2 minutes at a time)
• Inability to stand on a scale, i.e. permanently bedridden.
• Inability to cooperate with urine collection
• Receiving dialysis
• Terminal illness

The population consists of patients recruited from Aalborg University Hospital at the Department of Oncology.

No individual participant data will be shared because the data are personal and sensitive.