That there is probably a significant proportion of "cured" patients, particularly in the T1N0 group, is an important observation when one considers the proper role of adjuvant therapy, especially for patients with stage I disease. Analysis of this series indicates that patients with T1N0 disease can be subdivided into different prognostic groups. Factors associated with an especially favorable prognosis in T1N0 cases are a primary tumor size of 1 cm or less; special tumor type such as tubular, medullary, papillary, or colloid carcinoma; and low-grade tumor. Relatively unfavorable tumor characteristics are size greater than 1.0 cm (especially the group 1.7 to 2.0 cm), the presence of lymphatic tumor emboli in the breast, blood vessel invasion, high-grade tumor or poor differentiation, and intense peritumoral lymphoplasmacytic reaction. The T1N0 patients whose tumors manifest the latter features may have longer disease-free survival as a result of adjuvant therapy. On the other hand, women in the T1N0 group with an especially favorable prognosis usually can be spared adjuvant therapy.