Study shows 9‑week colon cancer response

Colon cancer is usually treated like a race against microscopic leftovers. Surgeons remove the tumor, then patients often get months of chemotherapy to mop up anything that might come back later. But a UK trial is pushing a different idea: hit the cancer first with a short burst of immunotherapy, then operate. In this specific group of tumors, that approach is looking unusually strong. ### What exactly changed? The new update came from the phase 2 NEOPRISM-CRC trial, led by University College London and University College London Hospitals. Researchers reported that 32 patients with high-risk stage II or III colorectal cancer carrying mismatch-repair deficiency — usually shortened to dMMR or MSI-high — stayed relapse-free for nearly three years after nine weeks of pembrolizumab before surgery. The median follow-up was about 33 months. (ucl.ac.uk) ### What is pembrolizumab doing here? Pembrolizumab is a PD-1 checkpoint inhibitor. Basically, it takes the brakes off immune cells so they can recognize and attack cancer more effectively. That matters a lot in dMMR/MSI-high tumors, because those cancers tend to carry lots of mutations and throw off more abnormal signals for the immune system to spot. This is not a generic colon cancer result — it is a result in a biologically selected subgroup. (ucl.ac.uk) ### Why is nine weeks such a big deal? Because standard colon cancer treatment is usually much longer and rougher. NEOPRISM-CRC used a short preoperative course instead of the usual pattern of surgery first and then months of postoperative chemotherapy. The appeal is obvious — if a brief immunotherapy run can shrink or even erase visible tumor before surgery, patients may avoid some of the toxicity and delay built into the older playbook. (clinicaltrials.gov) ### How strong were the responses? The headline efficacy number from the earlier readout was a 59% pathological complete response rate. That means no viable cancer was found in the surgical specimen after treatment. In plain English, the tumor was still there on scans or in the body plan, but under the microscope it had effectively been wiped out. And in the updated follow-up, researchers said no patient had relapsed. (ucl.ac.uk) ### Does this mean surgery is no longer needed? Not yet. Every patient in this trial still went on to planned surgery. That is important, because it means the study shows strong neoadjuvant — pre-surgery — activity, not proof that surgery can be skipped safely in colon cancer. The temptation is to jump straight to “just give the drug and watch,” but this dataset does not establish that. (aacrjournals.org) ### How big is the catch? The catch is size and selection. This was a 32-patient phase 2 study, not a definitive practice-changing phase 3 trial. And the patients were chosen for a subtype that is already known to be unusually immunotherapy-sensitive. That makes the result exciting, but it also means you should not generalize it to the average colon cancer case. (clinicaltrials.gov) ### Where does this fit in the bigger picture? It fits into a broader shift in dMMR colon cancer. Other studies, including NICHE-2, have already shown that short-course neoadjuvant checkpoint blockade can produce very high pathological response rates and excellent 3-year disease-free survival in this subtype. So NEOPRISM-CRC is not coming out of nowhere — it adds another signal that early immunotherapy may be moving toward a new standard for selected patients. (ucl.ac.uk) ### Bottom line? The real news is not “immunotherapy works in colon cancer.” We already knew that in advanced dMMR disease. The real news is that just nine weeks of pembrolizumab before surgery produced deep responses and, so far, zero relapses in this small high-risk group. That is the kind of result that makes larger trials feel less optional and more inevitable. (ucl.ac.uk) (annalsofoncology.org)