Validation of CTS5 on a Retrospective Cohort of Real-Life Pre- and Postmenopausal Patients Diagnosed With Estrogen Receptor–Positive Breast Cancers: Is It Prognostic?

More than 50% of estrogen receptor (ER)-positive breast cancer (BC) distant recurrences (DR) develop after the completion of 5 years of adjuvant endocrine therapy (ET). Its extension is beneficial on disease-free survival and overall survival but increases therapy-related side effects. Selecting patients who could benefit the most from an extended regimen has become an increasing need. Clinical Treatment Score at 5 Years (CTS5) is a prognostic tool using clinicopathologic data to estimate DR risk after 5 years of ET for ER+ BC. We sought to validate the prognostic value of CTS5 in a retrospective cohort of real-life pre- and postmenopausal patients diagnosed with ER+ BC. CTS5 was calculated for 603 patients diagnosed with ER+ BC at Umberto I Hospital of Turin and DR-free after 5 years of ET. Primary endpoint was late DR (LDR) rate. Median follow-up was 8 years (range, 6-26 years). The 426 postmenopausal women were categorized by CTS5 as follows: 152 low risk, 139 intermediate risk, and 135 high risk. LDR rates were 3.9%, 7.2%, and 15.6%, respectively. CTS5 results were prognostic for LDR: patients with CTS5-high showed a fourfold risk of developing an LDR compared to patients with CTS5-low (hazard ratio, 4.48; 95% confidence interval, 1.80-11.1). The same analysis was conducted for the 177 premenopausal women: 88 low risk, 40 intermediate risk, and 49 high risk. LDR rate were 5.6%, 7.5%, and 20.4%, respectively, proving CTS5 to be prognostic for premenopausal patients as well (CTS5-high vs. CTS5-low: hazard ratio, 3.40; 95% confidence interval, 1.06-11.0). CTS5 was shown to be prognostic of the risk of LDR in our population of real-life pre- and postmenopausal patients. Our results support its use in clinical practice to better tailor the prescription of extended ET. Clinical Treatment Score at 5 Years (CTS5) is an algorithm developed to identify patients with estrogen receptor–positive breast cancers at higher late distant recurrence (LDR) risk. We tested its clinical validity on a retrospective cohort of 603 real-life patients. CTS5 was shown to be prognostic on the risk of LDR for pre- and postmenopausal patients, supporting its use to better tailor the prescription of extended endocrine therapy.