Eduardo Vilar-Sánchez has spent more than 10 years pursuing a goal that seemed very distant, but which he now sees as a little closer: to develop a preventive vaccine against cancer.

The physician and researcher is leading a study that presented the first promising results of a colon cancer vaccine in a small group of patients suffering from a rare disease that makes them 17 times more likely to develop colon cancer than the general population. The trial results show that precancerous lesions had not grown a year after receiving the treatment and, more importantly, no new lesions had appeared.

This is a first indication that the vaccine, Nous-209, can help “prevent cancer before it appears,” according to a statement released Wednesday by the MD Anderson Cancer Center in Houston, USA, where Vilar Sánchez works.

“It is an initial step for the field, but we have shown that the development of preventive vaccines against cancer is feasible,” the 46-year-old Madrid-born doctor explains to EL PAÍS.

The trial focuses on a very small and specific population: patients with Lynch syndrome. This inherited genetic disorder affects approximately one in 270 people and significantly increases their risk of developing recurrent colon cancer throughout their lives.

The trial involved 45 patients with this syndrome who, at the time, had not developed colon cancer, but did have potentially precancerous lesions known as polyps. The Nous-209 vaccine consists of an inactivated monkey adenovirus that carries 209 antigens (proteins) that are frequently found in tumors of the colon, stomach and endometrium. In theory, this treatment helps the immune system recognize cancer cells.

The vaccine was well tolerated, with no serious treatment-related side effects. All participants developed robust T-cell immune responses capable of recognizing and attacking cancer-related targets, and these responses increased further with annual re-administration. In laboratory tests, the vaccine-induced T cells were able to eliminate tumor cells and showed signs of long-lasting immune memory. One year after treatment, researchers observed fewer precancerous lesions and no new advanced polyps in 85% of participants, providing “early evidence that NOUS-209 could help stop cancer before it develops.” The results are published in Nature Medicine.

This vaccine, or others like it, could be applicable to the general population. The tumors that develop in these patients are characterized by two DNA lesions known as mismatch repair deficiency and microsatellite instability. These same types of lesions appear in 15% of colon tumors, 20% of endometrial tumors, and 5% of bladder and stomach tumors.

Vilar-Sánchez discusses the implications of the results. “Clearly, the direct applicability is to the population with Lynch syndrome, which is relatively large, representing 3% of all colon cancers [there are one million patients with the syndrome in the United States alone]. In the future, it would also be applicable to the prevention of these cancers in the general population. Now, the challenge lies in identifying the risk groups, and that’s where the trick lies, because the development of preventive vaccines must go hand in hand with the development of risk identification strategies. The important thing is that we are taking a significant first step in this entire field,” he underscores.

The vaccine was developed by the Swiss pharmaceutical company Nouscom. The company and its U.S. medical team are already preparing larger clinical trials to compare the effectiveness of the immunization with randomized control groups in order to clarify the true effectiveness of the treatment.

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