High SLC20A1 Expression Is Associated With Poor Prognosis for Radiotherapy of Estrogen Receptor-positive Breast Cancer

Chotaro Onaga; Shoma Tamori; Izumi Matsuoka; Ayaka Ozaki; Hitomi Motomura; Yuka Nagashima; Tsugumichi Sato; Keiko Sato; Kouji Tahata; Yuyun Xiong; Yoshio Nakano; Yasunari Mano; Satoru Miyazaki; Kazunori Sasaki; Shigeo Ohno; Kazunori Akimoto

doi:10.21873/cdp.10126

High SLC20A1 Expression Is Associated With Poor Prognosis for Radiotherapy of Estrogen Receptor-positive Breast Cancer

Cancer Diagn Progn. 2022 Jul 3;2(4):429-442. doi: 10.21873/cdp.10126. eCollection 2022 Jul-Aug.

Authors

Affiliations

¹ Department of Medicinal and Life Sciences, Faculty of Pharmaceutical Sciences, Tokyo University of Science, Chiba, Japan.
² Department of Pharmacy, Faculty of Pharmaceutical Sciences, Tokyo University of Science, Chiba, Japan.
³ Department of Information Sciences, Faculty of Science and Technology, Tokyo University of Science, Chiba, Japan.
⁴ Laboratory of Cancer Biology, Institute for Diseases of Old Age, Juntendo University School of Medicine, Tokyo, Japan.

Abstract

Background/aim: Radiotherapy is one of the main treatments for estrogen receptor-positive (ER+) breast cancer. However, in some ER+ breast cancer cases, radiotherapy is insufficient to inhibit progression and there is a lack of markers to predict radiotherapy insensitivity. Solute carrier family 20 member 1 (SLC20A1) is a sodium/inorganic phosphate symporter, which has been proposed to be a viable prognostic marker for luminal A and B types of ER+ breast cancer. The present study examined the possibility of SLC20A1 as a novel biomarker for the prediction of radiotherapy efficiency.

Patients and methods: The Molecular Taxonomy of Breast Cancer International Consortium dataset was downloaded from cBioportal and the prognosis of patients with high SLC20A1 expression (SLC20A1 ^high ) was compared with that of patients with low SLC20A1 expression, without or with radiotherapy and tumor stages I, II, and III, using the Kaplan-Meier method and multivariate Cox regression analyses of disease-specific and relapse-free survival.

Results: Patients in the SLC20A1 ^high group with radiotherapy showed poor clinical outcomes in both luminal A and luminal B breast cancers. Furthermore, in luminal A breast cancer at tumor stage I, patients in the SLC20A1 ^high group with radiotherapy also showed poor clinical outcomes. Therefore, these results suggest that radiotherapy is insufficient for patients in the SLC20A1 ^high group for both luminal A and B types, and especially for the luminal A type at tumor stage I.

Conclusion: SLC20A1 can be used as a prognostic marker for the prediction of the efficacy of radiotherapy for luminal A and luminal B breast cancers.

Keywords: Breast cancer; ER+ breast cancer; SLC20A1; radiation resistance; radiotherapy.