The American College of Surgeons' long-term breast cancer survey in 1978 included 16,894 pathologically confirmed carcinomas of the female breast, in situ or infiltrative, with negative or positive nodes. Of these, 1.9% were in situ carcinoma of any size, and 8.4% were minimal invasive carcinomas 1 cm or less in diameter. No significant difference was found between the survival of patients with in situ tumors of any size and minimal invasive tumors with negative axillary nodes measuring 1 cm or less in diameter. In patients with invasive tumors with negative axillary lymph nodes, no statistically significant difference was found in survival of patients with tumors of 0.5 cm or less, when compared either with survival of patients with tumors measuring 0.6–1.0 cm. Recurrence rates observed in those groups were not statistically significant. Among 157 patients with invasive tumors measuring 0.5 cm or less, 23.0% presented with axillary lymph node metastasis. Tumors measuring 0.6 to 1.0 cm showed 20.9% positive axillary nodes in 964 patients. Statistically significant differences in survival and recurrence rates were achieved only for invasive tumors smaller than 1 cm. Survival and recurrence rates were significantly better (P < 0.001) in patients with minimal invasive cancer with negative axillary nodes (P < 0.001) than rates of patients with invasive tumors larger than 1 cm and with negative lymph nodes. Similar statistical results were obtained for patients with positive axillary nodes only for invasive cancers smaller than 1 cm. However, survival and recurrence rates observed in invasive cancers of 1 cm or less with positive axillary nodes suggest that tumor size alone cannot be used as the only defining criterion for minimal invasive breast cancer. Only the status of axillary nodes may determine whether a small invasive tumor below 1 cm may be considered as minimal breast cancer.