Abstract PO3-08-05: Prognostic value of multigene test to the patients with Hormone receptor-positive, HER2-negative breast cancer based on special histologic subtypes

Abstract Background: Special histologic subtypes of breast cancer, including mucinous and tubular, account for 25% of all invasive breast cancers. Multigene tests (MGT) play a crucial role in guiding adjuvant chemotherapy and predicting prognosis for the patients with Hormone receptor-positive HER2-negative breast cancer. This research aims to examine the results of multigene tests for special histologic subtype patients and review the prognosis of each group. Methods: A retrospective analysis was conducted on data from 133 patients with special histologic subtypes of breast cancer who underwent surgery at Severance Hospital between November 2013 and December 2022. Each patient underwent one type of MGT, including Oncotype Dx, MammaPrint, or EndoPredict. Patients were grouped in two groups according to histologic types, based on WHO classification. Favorable types consist of type A mucinous carcinoma, pure tubular carcinoma, invasive solid papillary carcinoma, encapsulated papillary carcinoma with invasion, invasive cribriform carcinoma, secretory carcinoma, and invasive carcinoma with apocrine differentiation. Unfavorable types included type B mucinous carcinoma, mucinous carcinoma with micropapillary feature or neuroendocrine differentiation, mixed IDC, ILC or invasive micropapillary carcinoma, mixed invasive solid papillary carcinoma, mixed invasive papillary carcinoma, and mixed invasive cribriform carcinoma with IDC. Results: Patients with favorable types accounted for 42.86% (57 patients), while patients with unfavorable types accounted for 57.14% (76 patients). Patients with unfavorable histologic subtypes of breast cancer tended to have a higher incidence of high-risk results in MGT, as well as a greater prevalence of multiple (multifocal, multicentric) cancer and higher histologic grade. In multivariate analysis using logistic regression, unfavorable types showed a significantly high ratio of having high risk on MGT compared to the favorable type (OR = 4.327, 95% CI 1.210 – 15.475, p-value = 0.024). Moreover, overall survival in unfavorable histologic types showed a statistically significant difference between high-risk and low-risk in Kaplan-Meier survival analysis (p-value = 0.001). Conclusions: Unfavorable subtypes have shown a significantly higher-risk result of MGT, and patients with unfavorable types of breast cancer and high-risk MGT results have exhibited the worst prognosis. Consequently, we can suggest that MGT can be used as a prognosis evaluation tool for certain special subtypes of breast cancer and further utilized to aid in treatment decisions. Citation Format: Seung Hye Yang, Jee Hyun Ahn, Suk Jun Lee, Jee Ye Kim, Hyung Seok Park, Seung Il Kim, Byeong Woo Park, Seho Park. Prognostic value of multigene test to the patients with Hormone receptor-positive, HER2-negative breast cancer based on special histologic subtypes [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 PO3-08-05.