In a a case of multiple colon cancers, I would think about a genetic syndrome.

Thank you for your answer.

I was asking about the case where the possibility of genetic syndrome is relatively low. For example, when two or three small tumors are located 4-5 cm away from each other and similar in size with no definite family history, no adenomatous polyps.

Multiple colorectal primaries are more common than mucosal metastases in this setting. An origin of each tumour from surface dysplasia is often able to be demonstrated in cases of synchronous CRC (as opposed to tumour colonising normal mucosa in a met, which is rarely seen), and synchronous tumours often have entirely differing morphologies. For tumours of differing size, these are still usually separate primaries in colon, unless good evidence for metastasis. Molecular profiling of the lesions might be helpful if there was doubt, though some difference can occur between primaries and metastases. Multiple primaries should raise suspicion for a familial cancer syndrome (such as Lynch Syndrome), but synchronous primaries can also occur sporadically likely due to generalised increased CRC risk due to combination of lifestyle risk factors, dietary carcinogen exposure and underlying genetic background.

Multiple synchronous colorectal cancers have to be assumed arising de novo in a generalized field defect of the colonic mucosa.

Thorough inspection of all areas of the colon with colonoscope with or without its optical adjuncts to highlight smaller and subtler lesions are essential.

Genetic studies of the resected lesions and adjacent mucosa are essential.