Every patient treated for rectal cancer with an experimental immunotherapy drug went into remission, in findings that researchers have hailed as a breakthrough. All 14 patients who were given the new drug, dostarlimab, were found after six months to have no trace of cancer. Researchers at Memorial Sloan Kettering cancer center in New York could find no sign of the disease through physical examination, endoscopies, MRIs or other scans. The researchers described the results, published in the New England Journal of Medicine, as “breakthrough findings” and said they were astonished by the universal success rate. “I believe this is the first time this has happened in the history of cancer,” Dr Luis Diaz, a leading member of the team, told the New York Times. For the patients involved – and potentially for other patients with specific types of rectal cancer who come after them – the outcome was dramatic. It allowed them to avoid further surgery, chemotherapy and radiation, proceeding under observation alone. That could have far-reaching implications, particularly for young adults. “Surgery and radiation have permanent effects on fertility, sexual health, bowel and bladder function and the implications for quality of life are substantial, especially in those where standard treatment would impact childbearing potential,” another lead researcher, Dr Andrea Cercek, said. “As the incidence of rectal cancer is rising in young adults, this approach can have a major impact.” Dostarlimab has been developed by the pharmaceutical company GlaxoSmithKline. The drug was given to the patients every three to six months at a cost of $11,000 each dose. The drug is known as a checkpoint inhibitor. It works by removing the shield that cancer cells put around them that blocks T-cells in the body’s immune system from attacking them. Without the shield, the cancer cells are exposed to the immune system and vulnerable to being destroyed. The findings fall within one of the most promising areas of frontier experimental cancer research that combines personalised medicine with immunotherapy. The ambition is to train the immune system to destroy cancer cells by helping it detect specific mutations in the genetic makeup of an individual patient’s own tumour. The Sloan Kettering researchers designed the clinical trial to apply to a specific sub-group of renal cancer patients. All 14 patients had a rare mutation in their tumour cells known as “mismatch repair deficiency”, meaning that the cells’ DNA repair system is not working. As a result, the cancer cells produce proteins with higher levels of genetic errors in them which makes them more visible to the body’s immune system once the shield has been removed. The scientists involved in the dostarlimab trial are at pains not to present the findings as a cure. The patients will be kept under close medical assessment to see how long they remain cancer-free. But they are optimistic about these first results. Diaz said the new treatment would be “practice-changing” for people with the relevant type of rectal cancer.