Colon Cancer Patients With Left-Sided Tumors Have Better Survival Rates Than Patients With Right-Sided Tumors

colon
Colon cancer patients with right-sided tumors have a worse prognosis than patients with left-sided tumors; this suggests the two halves of the human colon have different embryonic origins. Photo courtesy of Shutterstock.

The colon is divided into two halves, left and right, and while these two sides appear similar enough, more or less equal, a new study suggests this is not the case at all. When it comes to colon cancer, location matters: Patients with right-sided tumors have a worse prognosis than patients with left-sided tumors. This data suggests, then, that the two halves of the human colon have different embryonic origins.

Along with the division into left and right halves, the colon has four main sections: ascending (right) colon, transverse colon, descending (left) colon, and the sigmoid colon, which is considered to be part of the left colon. When you eat food, the partially digested contents travel from your small intestine up your ascending colon. Next, the contents move along your transverse colon before flowing down your descending colon and sigmoid colon. Having turned into feces along the way, what once was food finally enters your rectum in order to be expelled once and for all from your body. Not a pretty process, it is nevertheless a necessary one for sustaining life. And, like other bodily functions, it is only when something goes wrong that we understand it completely for the first time.

For instance, past studies have suggested quite a few differences between right- and left-sided tumors in situations of colon cancers. Generally, patients with right-sided tumors are older and more often female than patients with left-sided tumors. Right-sided colon cancers, for example, are often in a more advanced stage at diagnosis than left-sided colon cancers and they also have different molecular biological patterns. Some of these differences are explained simply by the colon’s anatomy. Compared to the left portion, the right colon is wider and so tumors tend to grow larger before causing symptoms. Right-sided tumors also tend to embed themselves within the wall and do not block the flow of feces unlike left-sided tumors, which often do. In the right colon, then, tumors tend to grow larger before causing symptoms so naturally, many doctors concluded this is what influenced different survival rates.

For the current study, the researchers sought to confirm a link between tumor location and prognosis in metastatic colon cancer (mCRC). They used data from three separate studies which included a total of 2,027 patients. The researchers assessed overall survival and progression-free survival for each of the patients and then analyzed the results.

They found nearly 70 percent of the patients had left-sided primary tumors and had better survival outcomes than those with right-sided tumors. They also found the efficacy of bevacizumab, a chemotherapy drug, to be independent of tumor location, though patients with right-sided tumors tended to develop chemoresistance more often, suggesting biological differences.

“These data demonstrate that primary tumor location is an important prognostic factor in previously untreated  mCRC,” wrote the authors. In an accompanying editorial on this research, Dr. Howard S. Hochster notes some caveats; however, he concludes "this interesting analysis gives rise to some important and testable biological hypotheses." In other words, this matter is worthy of more research, which certainly would be welcomed by colon cancer patients and their families.

Source: Loupakis F, Yang D, Yau L, et al. Primary Tumor Location as a Prognostic Factor in Metastatic Colorectal Cancer. JNCI: Journal of the National Cancer Institute. 2015.

Join the Discussion