A small cancer immunotherapy drug trial in patients with rectal cancer recently had an "unheard of" result: Every single patient treated achieved complete remission.

Why it matters: Based on just 12 patients, the trial was published Sunday in the New England Journal of Medicine and needs to be replicated in a much bigger study. But seeing complete remission in 100% of patients tested is a very promising early signal, researchers said.

• "I believe this is the first time this has happened in the history of cancer," paper co-author Luis A. Diaz Jr. of Memorial Sloan Kettering Cancer Center told the New York Times.

Details: Patients were given the drug known as a programmed cell death-1 or PD-1 inhibitor, or dostarlimab, to treat a certain type of locally advanced rectal cancer.

• After six months or more of follow-up, they continued to show no signs of cancer without needing standard treatments of surgery, radiation or chemotherapy.
• "It's incredibly rewarding to get these happy tears and happy emails from the patients in this study who finish treatment and realize, 'Oh my god, I get to keep all my normal body functions that I feared I might lose to radiation or surgery,'" said the principal investigator medical oncologist Andrea Cercek in a statement.

Yes, but: Again, this was a small study and not enough is yet known "to supplant our current curative treatment approach," an accompanying editorial pointed out.