After 1 year, more than 50% experience upper limb (UL) complaints after treatment for breast cancer. These complaints are disabling and cause limitations in daily life and this leads to a decrease in the patient's quality of life. The cause of these UL complaints is complex and multifactorial. Due to breast cancer treatment, the structural (tissue composition and volume) and mechanical (tissue stiffness) properties of the soft tissue may change. These changes can occur in the muscle, skin and surrounding fascia and especially in the soft tissue around the breast and axilla where that treatment is localised. Ultrasound with specific 'add-on' techniques can objectively assess these features and provide a picture of their role in UL function after breast cancer. The first aim in this study is to investigate the reliability and validity of conventional 2D ultrasound for 1) soft tissue composition and 2) soft tissue thickness at the level of the breast and upper limb. The reliability and validity of shear wave elastography, a specific complement to conventional 2D ultrasound, to assess tissue stiffness will also be examined.