Tumor size is the strongest predictor of axillary node metastases. Some authors have reported that axillary dissection in T1a breast cancer is not required because the rate of incidence is less than 5%. However I have doubts concerning the omission of axillary dissection in small breast cancers. Therefore, I investigated the incidence of axillary node metastases in T1 breast cancer according to size for the purpose of using this data as a reference for determining whether or not to dissect axillary lymph nodes.

Data of patients registered at the Strang Cancer Prevention Center affiliated with the New York Hospital-Cornell Medical Center, from January 1988 to December 1998 were reviewed. After review of charts and pathologic reports for tumor size, age at operation and lymph node status, 592 patients were proven to have primary breast tumor 2 cm in size or smaller. The size of the tumor was determined as the largest diameter of the invasive lesion when possible.

Lymph node metastases were seen in 7 of 68 cases in the 0.1~0.5 cm T1a (10.3%), 29 of 182 in 0.6~1.0 cm T1b (15.9%), 50 of 206 in 1.1~1.5 cm (24.3%) and 55 of 136 in 1.6~2.0 cm tumor size range (40.4%).

Although positive node occurrence was lower in small size tumors, significant number of patients with T1a invasive tumors have a positive node. Therefore, a small size of tumor alone is not an indicator for the omission of axillary dissection.