partial mastectomy segmental mastectomy http://purl.bioontology.org/ontology/MESH/D015412 http://purl.obolibrary.org/obo/NCIT_C20749 The removal of a neoplasm as well as some of the breast tissue around the tumor and the lining over the chest muscles below the neoplasm. Usually some of the lymph nodes under the arm are also taken out. segmental mastectomies