Abstract P3-01-05: The use of Tc-99 tilmanocept in sentinel lymph node biopsy after neoadjuvant chemotherapy in clinically node-negative patients with breast cancer

Background: Neoadjuvant chemotherapy (NAT) has been shown to induce fibrosis and inflammation that alters lymphatic drainage of axillary lymph nodes in breast cancer. Technetium- 99 Tilmanocept (TcTM), a CD206-macrophage receptor targeted radiopharmaceutical, is a small agent with recent FDA-approval for lymphatic mapping. No prior studies have investigated the use of TcTM in the neoadjuvant setting. The aim of this study was to compare the identification rate, node-positivity rate, and number of total nodes evaluated in sentinel lymph node (SLN) biopsy with TcTM and vital blue dye (VBD) in clinically node-negative patients receiving NAT vs. initial surgery. Methods: A retrospective review was conducted on patients undergoing SLN biopsy with TcTM and VBD from May 2013- May 2015 at UCSD. Patients with a history of prior SLN biopsy or axillary lymph node dissection were excluded. Patients undergoing neoadjuvant chemotherapy or receiving > 3 months of neoadjuvant endocrine therapy were grouped and compared to patients undergoing initial surgical treatment. The SLN identification and node-positivity rates were compared with the X2 test. To compare the number of SLNs evaluated between groups, a zero-truncated negative binomial (ZTNB) count model was constructed to assess the effect of NAT and other covariates on the SLN count. Covariates included age, body mass index (BMI), gender, surgeon, mastectomy vs. lumpectomy, node positivity, pathologist, T-stage, and receptor status. A p-value Results: Of the 417 total SLN cases identified, 72 (17.2%) cases were in patients who had received NAT (61- chemo, 11- endocrine). The SLN identification rate was 100% in both groups (p= 1.0). Overall, there were 68 (16.3%) cases of SLN-positivity, 14 (19.4%) in the NAT group versus 54 (15.7%) in the non-NAT group (p= 0.54). The median number of identified nodes was 3 in both groups. In the ZTNB count model, age, surgeon and evaluating pathologist were significant predictors of the total number of SLN evaluated. The use of NAT did not significantly affect the number SLNs evaluated. Incident rate ratios, confidence intervals and p-values are reported in the attached table. Discussion: Prior studies have indicated that NAT may induce fibrosis and inflammation that may obscure lymphatic mapping procedures. For SLN biopsy with TcTM in VBD in our study, the use of NAT did not change the identification rate or node-positivity rate. Additionally, when controlling for covariates, the use of NAT did not change the total number of SLNs evaluated. While NAT might induce fibrosis and inflammation, SLN biopsy with TcTM and VBD is technically successful in clinically node-negative patients undergoing neoadjuvant chemotherapy. Citation Format: Unkart JT, Wallace AM. The use of Tc-99 tilmanocept in sentinel lymph node biopsy after neoadjuvant chemotherapy in clinically node-negative patients with breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-01-05.