Author：Yane Song, Li Peng, Wei Zhou, Yiru Niu, Wanning Yang, Beibei Mao, Xianchao Guo, Wenbo Han, Henghui Zhang, Weizhi Chen, Feng Mao

Background: After primary surgical resection, quite a proportion of breast cancer survivors would experience local recurrence within 5 years. Whether local recurrent tumors arise independently or from the primary tumors, which is critical for diagnosis and appropriate treatment, remains a clinical dilemma. Phylogenetic analysis between the primary and recurrent tumor provides a new strategy helpful for determining the origin of the local recurrent tumor. 

Methods: DNA was extracted from FFPE samples of the primary and recurrent tumors from 12 patients with recurrence of ipsilateral breast tumor. Phylogenetic analysis between the primary and recurrent tumors in the same individual was performed based on whole exome sequencing. PyClone and SciClone were employed to detect subclones. 

Results: The median time to recurrence of the 12 patients was 15 months (9 to 52 months). 9 (75%) of the 12 patients recurred within 2 years. Each patient had one shared somatic mutation clone between the primary and recurrent tumor, with shared somatic mutation number ranging from 5 to 59. This observation suggests that the recurrent tumor maybe originate from the primary tumor. 

Conclusions: The shared somatic mutation clone indicates the primary and recurrent tumor could be of the same origin and the recurrent tumor was metastasis from primary lesion. This may provide some information to help selecting the most appropriate treatment for patients.