Incidence of Pathologic Nodal Disease in Clinically Node-Negative, Microinvasive or T1a Breast Cancers.

Background: Axillary staging in early-stage breast cancer can impact adjuvant treatment options but also has associated morbidity. The incidence of pathologic nodal positivity (pN+) in patients with microinvasive or T1a disease is poorly characterized and the value of sentinel node biopsy remains controversial.

Methods: Women with cN0 and pathologic microinvasive or T1a cancer who underwent upfront surgery were identified from the National Cancer Database. Pathologic nodal stage at the time of surgery was the primary outcome. Multivariable logistic modeling was used to assess predictors of pN+.

Results: Overall, 141,840 women were included; 139,206 had pathologic node-negative (pN0) disease and 2634 had pN+ disease. Rates of pN+ disease differed by receptor status, with the highest rates in hormone receptor-negative/human epidermal growth factor receptor 2-positive (HR-/HER2+) disease compared with triple-negative breast cancer (TNBC), HR-positive/HER2-negative (HR+/HER2-), and triple positive breast cancer. Rates of pN+ were also higher with lobular histology compared with ductal histology. Multivariable analysis demonstrated that compared with White women, Black women had higher odds of pN+ disease, and compared with women <50 years of age, women >70 years of age had higher odds of pN+ disease. Compared with women with HR+/HER2- disease, women with TNBC, triple-positive breast cancer, and HR-/HER2+ all had lower odds, and women with invasive lobular disease had higher odds compared with women with invasive ductal disease. Women with significant comorbidities also had higher odds of node positivity.

Conclusion: Over 90% of patients with clinically node-negative, microinvasive and T1a breast cancer remain pathologically node-negative following axillary staging. However, higher rates of nodal disease were found among Black patients, older patients, and patients with lobular cancer and significant comorbidities.