Stage IV colorectal cancer primary site and patterns of distant metastasis

- Tumors arising in the rectum were more likely to spread to the lungs than liver.
- Distal colon tumors were less likely to spread to one versus two visceral organs.
- Population-based data findings are consistent with previous clinical results.
- Observed metastatic patterns may relate to differences in venous drainage.

BackgroundAlthough colorectal cancer (CRC) usually metastasizes to the liver and/or lungs, factors influencing the anatomic pattern of metastases remain poorly understood.MethodsWe assessed the relationship between primary CRC site and pattern of synchronous metastasis among 1202 individuals diagnosed with incident metastatic CRC between 2010 and 2014 and identified through the Seattle-Puget Sound Surveillance, Epidemiology, and End Results (SEER) registry. Polytomous logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) for the association between primary tumor site and synchronous metastatic pattern.ResultsCompared to patients with proximal colon primaries, patients with rectal primaries were more likely to present with lungs-only or liver and lungs metastases versus liver-only metastases (ORlungs-onlyvs.liver-only: 2.39, 95% CI: 1.35-4.24, ORliver+lungsvs.liver-only: 2.20, 95% CI: 1.46-3.32).ConclusionThese findings suggest that patients with rectal primaries are more likely than patients with colon primaries to present with synchronous lung metastases.