"Game-changer": Immunotherapy highly effective against colon cancer, Dutch study finds

A short course of immunotherapy is highly effective in treating a certain type of colon cancer, researchers at the Antoni van Leeuwenhoek Hospital found in a study published in the New England Journal of Medicine. The treatment proved effective for almost all patients, with tumors completely disappearing for two-thirds of them. Their own immune systems had cleared up the cancer cells, the Netherlands Cancer Institute said.

The treatment consisted of two cycles of immunotherapy before surgery for patients with colon cancer with a specific genetic makeup, known as mismatch-repair deficient (dMMR) or microsatellite instable (MSI). At the time of surgery, 95 percent of patients had 10 percent or fewer cancer cells remaining. For 68 percent, there were no live cancer cells.

Medical oncologist Myriam Chalabi first did a small trial with this treatment on 20 patients four years ago. “We wanted to investigate what immunotherapy could do for people with non-metastatic colon cancer. We witnessed something that rarely ever happens: every single patient responded well to the new treatment.” That led to this larger study, which proved just as effective. “This treatment could be a game-changer,” Chalabi said.

The patients in the larger study have now been followed for around two years. “None of the patients saw recurrence even though many had high-risk tumors. The results are unprecedented. The efficacy as well as the side-effects are much better compared to chemotherapy before surgery, a treatment that only works in 1 out of 20 patients,” Chalabi said.

Immunotherapy is more effective than chemo on this specific type of colorectal cancer because it contains a high number of DNA errors, the medical oncologist explained. “That means that the tumor cells are more easily detected by the immune system. The immune system only requires a small incentive to successfully target the tumor cells.”

Towards the end of the year, the participants in this study will have been followed for three years. If the majority of these patients are still cancer-free, the researchers can push for making immunotherapy the standard treatment option for this type of colorectal cancer in the Netherlands. “That is what we are currently working towards. And eventually we hope to even provide the option of avoiding surgery in patients who respond well,” said Chalabi.