Circulating tumor cells in breast cancer with orthotopic allograft mouse model

Abstract

Breast cancer causes death not because of the primary tumor in the breast but because of metastases in distant sites that gradually cause organ dysfunction.1 Circulating tumor cells (CTCs) are cells that have detached from the primary tumor or metastatic tumor sited and entered the peripheral circulation.2 We established orthotopic breast cancer animal model of breast cancer with CTCs and validated the role of surgical treatment in the subjects with primary breast cancer without CTCs. (Materials and Methods) We implanted 1 ？104 GFP expressing 4T1 cells in 4th or 5th mammary fat pad of 8 week-old BALB/cAnNCrl mice(n=69). For the evaluation of role of surgery in early breast cancer with no CTC, we removed the tumor cell just before CTCs appeared in circulation (n=35). After removal of the primary tumor we evaluated the extent of surgical procedures. If there was any suspected residual tumor tissue in operation bed, the procedure was categorized as R1 resection. If operation bed was not suspected with residual tumor tissue, the resection was categorized as R0 resection.(Results) All the experimental animal showed CTCs after primary tumor appeared (n=69). Furthermore, tumor volume and the number of CTCs increased over time and tumor volume showed statistically significant correlation with CTCs (p<0.001).Next, we removed primary tumor before a CTC was detectable with flow cytometry assay (n=35). The mice showed no CTCs during follow up if removal of the tumor results in complete resection of the tumor, R0 resection (n=25). However, we could detect CTCs during follow up period if the resection results in simple wide excision, R1 resection (n=10) (p<0.001).(Conclusions) We successfully developed orthotopic allograft mouse model with breast cancer and circulating tumor cells, which is most similar with human breast cancer evolution. We also showed R0 resection of the primary tumor could result in no CTCs during follow up period if the resection was done when there was no CTCs. We believe this finding could be translated in the clinical field.