Studies Show Colon Cancer Tumors that Originate on Opposite Side Respond Differently
In just the past couple of years, studies have found what many consider surprising data showing different responses to treatment between colon cancer tumors that originate on the right side of the colon versus those that grow on the left.
Those discoveries are driving development of treatment approaches that are targeted to particular cancers within the colon. And knowing the differences in how right-side and left-side colon cancer tumors respond to treatment is helping oncologists make individualized treatment plans for colon cancer patients, says Rocky Mountain Cancer Centers oncologist Sujatha Nallapareddy, MD.
The findings emerged most clearly in 2016, when researchers presented a study that looked back at treatment outcomes for colon cancer patients, and found a clear pattern: treatment success was greater for patients whose tumors originated on the left.
Additional research has quickly expanded on that knowledge, says Dr. Nallapareddy. “We see that right-sided tumors are more aggressive compared to those on the left.” In addition, studies have shown that the side a tumor originates on may determine how it responds to certain chemotherapy drugs.
Right-Sided vs Left Sided Colon Cancer Tumors
Generally, right-sided colon cancer consists of cancers of the ascending and transverse colon. Left-sided colorectal cancer consists of cancers of the descending colon, along with the rectum. The ascending colon sits on the right side of the abdomen, rising from the appendix and reaching up toward the chest until it folds to the left and becomes the transverse colon. The transverse colon crosses the abdomen from right to left, then bends and becomes the descending colon. The descending colon stretches down along the left side of the abdomen to the rectum.
All the reasons for the differences in left-side and right-side tumors still aren’t clear, but research is shedding new light on some potential causes, Dr. Nallapareddy says:
- The different sides of the colon develop from different embryonic cells in the womb. And after formation, the right side of the colon has a different blood source than the left.
- Right-sided tumors are more likely in patients who have a genetic predisposition to colorectal cancer, including those with Lynch syndrome or micro¬satellite instability. Microsatellite instability is a genetic predisposition to greater than average occurrence of mutation.
- Tumors with BRAF mutations, which are a poor prognostic sign in colorectal cancer, also are more likely to occur on the right side.
- The gut microbiome – the collection of genes and bacteria – appears to be different on the right and left sides of the colon. “The right side seems to have more colonization of bacteria,” Dr. Nallapareddy says.
One advantage to right-side colon cancer tumors is that early-stage tumors can be removed more easily than those on the left, Dr. Nallapareddy says.
Most importantly, oncologists treating colon cancer have far more knowledge about the disease, and many more weapons in their arsenal than they did even a decade ago.