NCIt definition : Stage IB includes: (T0, N1mi, M0); (T1, N1mi, M0). T0: No evidence of primary tumor.
T1: Tumor 20 mm or less in greatest dimension. T1 includes T1mi. T1mi: Tumor 1 mm
or less in greatest dimension. N1mi: Nodal micrometastases. M0: No clinical or radiographic
evidence of distant metastasis. M0 includes M0(i ). (AJCC 7th Ed.);
Alternative definition : NCI-GLOSS: Stage I breast cancer is divided into stages IA and IB. In stage IB, (1)
no tumor is found in the breast, but small clusters of cancer cells (larger than 0.2
millimeter but not larger than 2 millimeters) are found in the lymph nodes; or (2)
the tumor is 2 centimeters or smaller and small clusters of cancer cells (larger than
0.2 millimeter but not larger than 2 millimeters) are found in the lymph nodes.;