Abstract Background: Anastomotic recurrences occur in 2-10% of colorectal carcinoma (CRC) cases after surgical resection of the primary tumor. To date there are no molecular data investigating their genetic profile and multiple theories exist as to their pathogenesis including re-growth of tumor cells present within local lymphatics after initial surgery, seeding of anastomosis by metastatic tumor cells and a second primary tumor. The aim of our study was to compare the genomic profile of anastomotic recurrences to that of matched primary tumors and, where available, to that of distant metastases. Design: Thirty-six tumors from 14 patients were genotyped using a hybridization capture-based next-generation sequencing assay for targeted deep sequencing of all exons and selected introns of 341 key cancer genes. All patients had resection of their primary tumor with clear margins and recurred either at the anastomotic line or in the peri-anastomotic area 1.1 to 7.0 years following resection of their primary tumor. In 3 patients 2 consecutive anastomotic recurrences were sequenced, while in 6 patients a distant metastasis that occurred 1.2 to 3 years prior to the anastomotic recurrence was also analyzed. All tumors were microsatellite stable except in one patient with genetically confirmed Lynch syndrome. Results: A total of 254 somatic mutations were detected including 140 mutations in the microsatellite stable cases. The most commonly mutated genes (mutated in > 3 patients) were APC, KRAS, TP53, PIK3CA, ATM and PIK3R1. In 13/14 patients the anastomotic recurrence(s) and primary tumor shared between 50-100% of mutations, including mutations in key driver genes such as APC, KRAS and TP53, consistent with these tumors being clonally related. In the patient with the Lynch syndrome the 2 tumors showed distinct somatic mutations suggestive of independent primaries. We identified eleven genetic events present in a distant metastasis and not in a primary tumor and none of these events was detected in the anastomotic recurrence arguing against re-seeding of the anastomotic site by a metastatic clone. All five patients with isolated anastomotic recurrence were free of disease 0.9 to 6.1 years following resection of their recurrent CRC. Conclusions: Anastomotic recurrences appear to be clonally related to the primary tumor in sporadic CRC cases. Our data also provide molecular data in support of the treatment of anastomotic recurrences as localized disease. Citation Format: Efsevia Vakiani, Ronak H. Shah, Christine Iacobuzio-Donahue, David B. Solit, Martin R. Weiser. Anastomotic recurrences are clonally related to primary tumors in sporadic colorectal carcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2419.