Unlike colon cancer, rectal cancer has unique characteristics that make preoperative “chemo-radiotherapy” a popular treatment option, enabling 10-15 percent of patients with advanced rectal cancer to achieve a "complete remission," meaning the cancer is completely gone.

Unlike the colon, the rectum does not have an intestinal lining and has many blood vessels around it, so there is a higher risk that rectal cancer can spread more widely and quickly than colon cancer.

On the other hand, since rectal cancer is located in the pelvis, it is difficult to surgically resect a large area like colon cancer, so preoperative chemotherapy and radiotherapy are often used to reduce the size of the tumor and increase the chances of preserving the anal sphincter, which is why some patients with advanced rectal cancer are cured without surgery.

“Some 10 to 15 percent of patients with rectal cancer can be completely cured of it with preceding radiation and chemotherapy," said Dr. Hwang Dae-yong, a professor at the Colorectal Cancer Center at Konkuk University Medical Center, noting that one in seven to 10 patients with advanced rectal cancer who try upfront radiation and chemotherapy achieve complete remission.

In the past, although preceding chemotherapy and radiation eliminated the cancer, there was a push for surgery because the cancer cells were thought to be still around, if invisible. However, this is no longer the case, according to Professor Hwang.

As studies have shown that patients are cured of rectal cancer with upfront chemotherapy and radiation, the current treatment approach is to let doctors follow up with it to make sure that the rectal cancer is completely gone after upfront chemotherapy and radiation, he explained.

"In 2015, we published data on this at the Sloan Kettering Cancer Center in the U.S. and found that the stable condition continued in 75 percent of such patients. In about 25 percent, the tumor regrew, but it was not too late to do surgery then," Hwang said.

In addition to endoscopy, he recommended a rectal resection to determine if the rectal cancer had completely disappeared after prior chemotherapy and radiation.

"It's most important to feel where you can feel," Hwang said.

He explained that the medical community has concluded to continue to observe the rectal cancer area in addition to the endoscopy if there is no rectal cancer. However, the problem of confirming that it is completely gone has become the homework for medical professionals.

Of course, 25 percent of patients with advanced rectal cancer in complete remission after upfront chemotherapy and radiation can grow cancer again, and since it is not possible to identify which patients with advanced rectal cancer will grow cancer again, all patients must be followed up at the hospital periodically.

"One patient who reached complete remission after upfront chemotherapy and radiotherapy, the cancer grew again about a year later, and we had to perform surgery to expose the entire anus," Hwang said, emphasizing that the patient is doing well.