Cancer patients treated with a pioneering immunotherapy that genetically modifies their own cells to wipe out tumors live 40% longer, according to “exciting” and “groundbreaking” results from a world-first clinical trial, The Guardian reports.

Car T-cell therapy is a new form of immunotherapy where a patient’s own T-cells—a type of white blood cell—are tweaked in a lab to target and kill cancer cells. The designer cells are then infused back into their bloodstream to fight the disease.

In the trial hailed as a “milestone” by experts, patients with advanced gastric or gastro-esophageal junction (GEJ) cancer treated with Car T-cell therapy lived on average approximately 40% longer than patients who received standard care.

The results were published in The Lancet and presented at the world’s largest cancer conference, the annual meeting of the American Society of Clinical Oncology (Asco), in Chicago.

The therapy has already proved successful in treating blood cancers.

Now results from the world’s first randomized controlled trial of Car T-cell therapy in solid tumors suggest it could be transformative in the fight against these cancers too.

Solid tumors represent about 90% of all cancers, including breast, lung and pancreatic cancer.

In the trial, more than 100 patients in China with advanced gastric or GEJ cancer were randomized to receive either Car T-cell therapy or one of the standard-of-care medications.  Patients who received Car T-cell therapy lived an average of 7.9 months after randomization, compared with 5.5 months through standard care.