Tumor Seeding During Colonoscopy May Cause Subsequent Metachronous CRC

Primary tumor cells may be seeded in damaged mucosa during colonoscopy to biopsy a primary tumor, increasing the risk for metachronous CRC.

Post resection of colorectal cancer (CRC), patients undergo surveillance colonoscopy due to the risk of recurrent and metachronous CRC. Primary tumor cells may be seeded in damaged mucosa during colonoscopy to biopsy a primary tumor, increasing the risk for metachronous CRC, according to study results published in Gastroenterology.

In this study, researchers examined patient records from the Dutch National Pathology Registry to identify potential mechanical tumor seeding cases and to quantify the risk of iatrogenic tumor seeding during endoscopic procedures. The study examined clinical and pathology records from 2013 to 2015 for surgically treated patients with CRC who had a recurrence of CRC within 6 to 42 months postsurgery (N=2147).

The researchers identified patients as being at potential risk for mechanical tumor seeding if they had endoscopic manipulations such as biopsy or polypectomy of the primary tumor followed by other interventions in the colorectum after primary tumor manipulation during the same procedure. A total of 310 patients met these criteria.

Pathology reports revealed that among the 22 cases of metachronous CRC, 5 were likely caused by tumor seeding. Of these 5, tumor tissues were available for 3 cases. Targeted next-generation sequencing was performed on material from the primary tumor, the metachronous tumor, and from polyps removed during colonoscopy from the same location as the subsequent metachronous tumor. Results showed identical molecular profiles for the primary and metachronous colorectal tumors. In 5 control cases with a different etiology of metachronous CRC, the molecular fingerprint of the primary and metachronous tumors were completely different.

Based on clinical review of the 2147 records that met inclusion criteria, researchers estimated the risk of tumor seeding during colonoscopy at between 0.3 and 0.6%. Researchers also showed that during biopsies, the working channel of the endoscope and instruments placed in the working channel can become contaminated with tumor cells. These tumor cells were shown to maintain their ability to grow and multiply in organoid cultures.

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The study had 2 main limitations. There was no tumor material available for 2 of the suspected tumor seeding cases; therefore, molecular analysis could not be performed for those cases to determine cause. Additionally, the estimated risk of mechanical tumor seeding based on clinical review of patient records was inexact because it did not account for variables such as level of surgical expertise, the type of instruments used, or type of hospital setting.

The researchers concluded that the study experiments “provide a proof-of-concept of mechanical tumor seeding during colonoscopy.” While the risk for iatrogenic seeding during colonoscopy is low, results of this study may promote greater awareness of this potentially preventable cause of metachronous CRC.

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.


Backes Y, Seerden TCJ, van Geste RSFE, et al. Tumor seeding during colonoscopy as a possible cause for metachronous colorectal cancer [published online August 13, 2019]. Gastroenterology. doi: 10.1053/j.gastro.2019.07.062.