Survival Time and Molecular Subtypes of Breast Cancer after Radiotherapy in Thailand

Background: Breast cancer is an important cause of death among women. One way of classifying differentforms of breast cancer is by molecular features, usually in terms of the four subtypes: luminal A, luminalB, HER2-enriched, and triple negative.
Objectives: This study aimed to investigate the association betweenmolecular subtypes and survival among breast cancer patients treated with radiotherapy. Materials and
Methods:A retrospective cohort study was conducted. The subjects were 272 breast cancer patients who had receivedtreatment in the radiotherapy unit at Srinagarind Hospital, Thailand, between 1 January, 1999, and 31 May,2009. The end of the study was 1 June, 2014. Overall survival was defined as the time elapsing between initialregistration at the radiotherapy unit and death or the end of the study. Survival curves were estimated by theKaplan-Meier method, and a multivariate analysis was performed using Cox’s proportional hazard regressionmodel.
Results: The patient mean age was 47.5±10.4 at the time of diagnosis. Of the 272 patients, 146 (53.7%)were classified as luminal A, 12 (4.4%) as luminal B, 30 (11.0%) as HER2-enriched, and 84 (30.9%) as triplenegative. The overall survival rates at 1, 3 and 5 years were 87.1%, 68.4% and 59.2%, respectively. According tomolecular subtypes, HER2-enriched patients had the lowest 5-year survival rate (30.0 %, 95%CI: 15.02-46.55).The median follow-up time was 8.37 years. In the Cox model analysis a higher risk of death was found for patientswith HER2-enriched (HRadj=3.34, 95%CI:1.96-5.67), triple negative (HRadj=2.17, 95%CI: 1.44-3.27), and stageIIlB (HRadj=2.20, 95%CI: 1.16-4.17) cancers.
Conclusions: The worst survival rates were among patients classifiedas HER2-enriched, triple negative and at stage IIIB. Early detection and an advanced treatment modality areneeded to help these patients.