Abstract PO3-02-11: Impact of Tumor Volume on Oncologic Outcomes in Patients with T1 Breast Cancer: A Retrospective Analysis

Abstract Backgrounds: Measuring the extent of tumor cell accretion in the primary organ typically involves assessing the longest diameter, an important component of the widely employed TNM staging system. The largest tumor diameter is considered indicative of the risk of cancer metastasis and the likelihood of distant recurrences. However, relying solely on the unidimensional diameter to determine the degree of cancer cell accretion can be inadequate since each tumor has a unique three-dimensional shape, thus leading to different tumor volumes. Purpose: The aim of this study was to investigate the impact of tumor volume on oncologic outcomes in patients with T1-2 breast cancer. Method: We retrospectively reviewed the medical records of 1,018 patients diagnosed with invasive breast cancer who underwent breast-conserving surgery at Seoul National University Bundang Hospital from 2010 to 2015. Patients with multiple tumors, positive margins leading to mastectomy, or those who received neoadjuvant chemotherapy were excluded. Tumor volume was defined as the product of the length of the three axes to simplify the calculation. Recurrence-free survival (RFS) was estimated by the Kaplan-Meier analysis. Result: The median value for tumor volume was 7.502 cm³. Out of 1,018 patients, 124 patients exhibited tumor volumes greater than the median value. Higher tumor volume was associated with pathologic T stage (P < 0.001), pathologic N stage (P = 0.004), histologic grade (P < 0.001), and luminal B subtype (P = 0.008). In multivariable logistic regression analyses for recurrence, higher tumor volume (OR 3.532, 95% CI 1.708-7.303, P = 0.001), CEA elevation (OR 6.129, 95% CI 1.497-25.092, P = 0.012), pN stage (OR 2.038, 95% CI 1.005-4.132, P = 0.048), and luminal B subtype (OR 2.407, 95% CI 1.060-5.470, P = 0.036) were shown to be predictive factors for recurrence, while completion of radiation therapy (OR 0.142, 95% CI 0.050-0.402, P < 0.001) and completion of hormone therapy (OR 0.200, 95% CI 0.047-0.849, P = 0.029) were identified as protective factors. The 5-year RFS was significantly lower in patients with higher tumor volume compared to those with lower volume (97.4% vs. 91.9%; p < 0.001). In multivariable Cox regression analysis, tumor volume (HR 3.056, 95% CI 1.572-5.940, P = 0.001), CEA elevation (HR 4.934, 95% CI 1.437-16.935, P = 0.011), luminal B subtype (HR 2.336, 95% CI 1.076-5.073, P = 0.032), completion of RT (HR 0.131, 95% CI 0.053-0.325, P < 0.001), and completion of HTx (HR 0.199, 95% CI 0.060-0.655, P = 0.008) were identified as independent prognostic factors for RFS. Conclusion: In the current study, we showed higher tumor volume results in poorer oncologic outcomes in patients with T1-2 breast cancer. Therefore, the T stage based on tumor volume, which includes all three-dimensional measurements, can better predict the prognosis in breast cancer patients than the traditional T stage that is solely dependent on the unidimensional longest tumor diameter. Citation Format: Hyoung Won Koh, Eun-Kyu Kim, Hee-Chul Shin. Impact of Tumor Volume on Oncologic Outcomes in Patients with T1 Breast Cancer: A Retrospective Analysis [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-02-11.