The modes of growth and extension of breast cancer have been evaluated in operated specimens. It has been found that in patients with a cancer in the duct, the outcome was more closely related to the degree of the extraductal infiltration than the size of the tumor. If early breast cancer is defined as a cancer associated with a 10-year survival rate of 90% or more then lesions of the intraductal type with an extraductal infiltration of less than 1/4 of the entire tumor extension fall into this category.