This study aimed to validate the Clinical Treatment Score post-5 years (CTS5)-based risk stratification in a cohort comprising pre- and postmenopausal patients with estrogen receptor (ER)–positive breast cancer. We investigated the clinicopathologic parameters including Ki-67 labelling index (LI) to identify factors affecting late distant recurrence (DR). Women with ER-positive breast cancer who were free of DR for 5 years were identified between January 2004 and December 2009. We investigated the risk of late DR (5–10 years) according to the CTS5 risk group. Cox regression analysis was used to determine the prognostic performance of CTS5 and identify factors associated with late DR. In all, 680 women were included. Of these, 379 (55.7%) were premenopausal and 301 (44.3%) were postmenopausal. At a median follow-up of 118 months, 32 women had late DR. CTS5 was a significant prognostic factor for late DR in both pre- and postmenopausal women. In the low CTS5 group, high Ki-67 LI (> 20%) was a significant risk factor for late DR. CTS5 is a useful tool for assessing the risk of late DR in pre- and postmenopausal women with ER-positive breast cancer. Extended endocrine therapy can be considered in patients with high Ki-67 LI (> 20%) in the low CTS5 group.
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