WordNet (r) 3.0 (2006):

mastectomy
    n 1: surgical removal of a breast to remove a malignant tumor

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "mastectomy":
   adenoidectomy, appendectomy, arteriectomy, castration,
   cholecystectomy, craniectomy, cricoidectomy, cystectomy,
   enterectomy, gastrectomy, hemorrhoidectomy, hysterectomy,
   mammectomy, mastoidectomy, nephrectomy, omphalectomy, oophorectomy,
   oophorocystectomy, orchidectomy, ovariectomy, pancreatectomy,
   penectomy, pericardiectomy, phrenicectomy, pneumonectomy,
   prostatectomy, salpingectomy, stapedectomy, tonsillectomy,
   ureterectomy, urethrectomy, vasectomy, venectomy