P027 Establishment of a Thai patient-derived breast cancer organoid biobanking for drug screening in a single medical center in Thailand

Results: Of 4010 breast cancer patients, 215 (5.3%) had BBC.Of these, 106 (49%) were classified as having MBBC and 109 (51%) as SBBC.The median follow-up time for MBBC and SBBC groups was 117 and 43 months, respectively.SBBC patients were older than MBBC patients at the time of their first cancer detection by 4.4 years on average ( p = 0.007).SBBC patients also had a significantly higher cancer stage at first detection as compared with MBBC patients, but without a clear difference in cancer subtype.Under the hypothesis that MBBC and SBBC were the same cancer, lead time bias was defined as the time to second cancer in the MBBC group, which was 7.2 years on average.After adjusting for lead time bias, there was no significant difference at the 5% level in terms of overall survival distant diseasefree survival between the 2 groups, based on both the log-rank test and Cox's proportional hazards model.Conclusion(s): Clinical differences (and similarities) between synchronous and metachronous BBC can be largely explained by leadtime bias and late detection under the hypothesis that they are similar types of cancer.