The invention relates to a marker body (10) for marking
breast tissue for radiotherapy. The marker body (10) has an at least partly tube-like body (12) which is made from a soft elastic material and carries multiple radio-
opaque marker elements (18). The at least partly tube-like body (12) is designed so that it offers hardly any resistance to an external, deforming force, but returns to its original shape in the absence of external forces. The at least partly tube-like body (12) has two free longitudinal ends (14, 16) which can be detachably interconnected or are interconnected, resulting in a tubular ring.