Abstract 183P
Background
The rate of late distant recurrence of hormonal receptor (HR) positive breast cancer continued steadily even after 5 years of endocrine treatment. Clinical Treatment Score post-5 years (CTS5) was developed and validated as a tool to assess the risk of late distant relapse (LDR) using data from ATAC and BIG1-98. This study aimed to externally validate CTS5 in a real-world cohort of HR positive breast cancer patients diagnosed and treated at an academic center in Thailand.
Methods
This is a retrospective analytical research of early-stage, HR positive breast cancer patients, who completed 4.5-5.5 years of adjuvant endocrine therapy without recurrence. Primary endpoint was late distant relapse. The risk of LDR was determined using CTS5 calculator. Cox regression model and Kaplan-Meier survival analysis were applied for prognostic validation of CTS5. Calibration was performed by comparing the observed to expected LDR using Hosmer-Lemeshow test (H-L)
Results
A total of 323 women were included in the analysis with a median follow-up of 11.6 years. The average age is 51 years old; 54.2% were post-menopausal and over 2/3 received adjuvant chemotherapy. Rate of LDR events was 10.8%. According to CTS5, 48% were categorized as low-risk, 28.5% as intermediate-risk, and 23.5% as high-risk for LDR. The CTS5 was prognostic for LDR in our population with HR of 2.1 (log-rank, p <0.001) for each unit increase in score and a significant difference in LDR between intermediate and high-risk groups compared to low risk group. C-index of the area under ROC curve was 0.672 for entire cohort, 0.72 in post-menopausal group and 0.62 in premenopausal group There was no significant difference between actual and expected number of LDR events with O/E ratio of 0.99 (0.86-1.12) (H-L p = 0.79) indicating a proper calibration in this cohort of patients.
Conclusions
Our study validated that CTS5 is accurate in predicting the risk of LDR in HR positive breast cancer in Thai patients. Its performance seemed to be better in post-menopausal patients. CTS5 could be applied to routine clinical practice to compliment the decision toward prolonged endocrine therapy in intermediate and high-risk patients.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
Division of Medical Oncology, Department of Internal Medicine, Ramathibodi Hospital, Mahidol University.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.