Cancer of the breast in subjects 40 years of age or under is not a rare occurrence. A recent survey of the admissions to the Memorial Hospital from Jan. 1, 1917 to Jan. 1, 1929 showed that 2,663 patients with cancer of the breast had sought admission during this period.1 The research further revealed that 17.33 per cent (or approximately one sixth) of all patients with cancer of the breast were 39 years or younger. The incidence of mammary cancer in persons in the younger age periods must be borne in mind, otherwise errors in diagnosis will inevitably occur and unfortunate end-results follow. The material for this paper was furnished by a study of 303 patients admitted to the breast clinic of the Memorial Hospital prior to November, 1926. Radical mastectomy was performed on 191 patients, presenting presumably operable cases at the time of operation. In 44 a radical