Abstract Background: The presence of axillary nodal metastases is a poor prognostic indicator in patients with breast cancer. In the majority of patients, axillary nodal involvement correlates with tumor size and most commonly in tumors greater that 1 cm. Many series report an incidence of axillary nodal metastases in 3–37% of patients with tumors less than or equal to 2 cm. The presence of axillary nodal metastases will often change the stage of the cancer and role of adjuvant systemic treatment; therefore, it is important to understand what features are associated with these small lymph node positive tumors. The purpose of this study is to identify characteristics of T1a and T1b breast cancers that present with axillary nodal metastasis. Methods: A retrospective review of a prospective database identified 878 patients with T1a and T1b breast cancer. Pathologic features including tumor grade, hormone receptor status, lymphatic and vascular invasion, Her-2 neu status, and tumor histology were examined in patients with and without axillary nodal metastases. Pearson's χ2 test along with stepwise linear regression analysis were used to determine which factors were associated with the development of axillary nodal metastases. Results: There were 289 T1a lesions and 589 T1b lesions studied. Four independent variables were found to be associated with axillary nodal metastases in T1a-T1b breast cancer. As illustrated in Table 1, a significant difference was seen in nodal positivity among patients with ER negative tumors compared to those with ER positive tumors (p=.0000). An increased incidence of nodal positivity was also observed among patients with LVI compared with those without LVI (p= .0000). A significant difference was observed in nodal positivity among patients with perineural invasion compared to those without (p=.0006). An increased incidence of nodal positivity was also observed among T1a and T1b tumors with a higher histologic grade (p= 0409, p= .0001). Of note, when comparing T1a to T1b breast cancers, there was no significant difference found among the identified exposure variables of interest. Conclusion: In this series, the overall prevalence of nodal positivity in T1a and T1b breast cancer is 12%. An absence of a relationship between T1a and T1b cancers with nodal positivity was observed. However, the presence of nodal positivity showed a significant correlation with ER negativity, LVI, perineural invasion, and higher histologic grades. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-09-16.