ALBANY, NY — More than 95,000 Americans develop colon cancer, making it the third most common cancer in the U.S., excluding skin cancers. While stage and histology are known to affect prognosis, does it matter where tumors first occur in the massive organ?

According to research released in conjunction with this weekend’s 2018 American Society of Clinical Oncology Annual Meeting, location makes a significant difference.1

A team of researchers from the Stratton VAMC and the Albany Medical College, both in Albany, NY, analyzed data from the National VA Cancer Cube Registry to detect differences in the course and characteristics of colon cancer based on tumor sidedness. They defined right-sided colon cancer as tumors that first appeared in the region from the cecum to the hepatic flexure. Left-sided colon cancer included those that originated from the splenic flexure to the rectum. Transverse cancer included all those that arose between the flexures.

The researchers identified 65,940 total cases of colon cancer diagnosed in veterans who received care at VA facilities between 2001 and 2015. Of those, they classified 30.1% as right-sided and 58.8% as left-sided colon cancers.

Right-sided colon cancer arose more frequently in women, in whom it accounted for 36.3% of cases, compared to 30.1% of cases in men. Right-sided colon cancer also represented the majority (51.8%) of cases in patients over the age of 70, while about one-third of older patients developed left-sided colon cancer. Left-sided colon cancer occurred slightly more often in whites (59.4%) than in blacks (56%).

Right-sided colon cancer was more likely to have reached an advanced stage prior to diagnosis; 60.84% of cases were diagnosed as stage II-IV. In left-sided colon cancer, by contrast, nearly half of cases (48.2%) were stage I at diagnosis.

Notably, right-sided colon cancer has a worse one-year survival rate than left-sided colon cancer. The majority of patients with right-sided colon cancer (50.5%) died within the first year after diagnosis compared to 42.2% of those with left-sided colon cancer.

1Azar I, Esfandiarifard S, Virk G, et al. Primary tumor sidedness in colorectal cancer at VA hospitals: A nation-wide study. J Clin Oncol 36, 2018 (suppl; abstr e15638).