In the cases reported here there were found certain clinical and histologic features not shared in their entirety by other, probably closely related, lymphoblastomatous diseases. REPORT OF CASES Case 1.—History.— Mrs. J. O., a housewife, aged 58, who was referred by Dr. J. Homer Cudmore, when first observed on Nov. 24, 1933, complained of a steadily enlarging mass on her right breast. The duration was three months. There were no subjective symptoms. The familial and the personal history were unimportant. Physical Examination.— The patient was 20 pounds (9.1 Kg.) overweight, but was otherwise in good health. Examination of her skin disclosed an oval-shaped, elevated mass, measuring 3 by 2 cm., situated 2.5 cm. below and to the mesial side of the right nipple, the long axis being lateral (fig. 1). The affected area was bright red. The surface was smooth but irregular. On the surface near the inner