Sniffer dogs can be used to reliably detect lung cancer, according to researchers in Germany. Writing in the European Respiratory Journal, they found that trained dogs could detect a tumor in 71 percent of patients, BBC News reported Thursday.

However, scientists do not know which chemical the dogs are detecting, which is what they say they need to know to develop a screening program.

Cancer Research UK said that was still a "long way" off, the broadcaster said.

It was first suggested that dogs could "sniff out" cancer in 1989 and further studies have shown that dogs can detect some cancers such as those of the skin, bladder, bowel and breast.

It is thought that tumors produce "volatile chemicals" which a dog can detect, the report said.

Researchers trained four dogs, two German shepherds, an Australian shepherd and a Labrador, to detect lung cancer.

Three groups of patients were tested: 110 healthy people, 60 with lung cancer and 50 with chronic obstructive pulmonary disease, a narrowing of the airways of the lungs.

They all breathed into a fleece filled tube, which absorbed any smells.

The dogs sniffed the tubes and sat down in front of those in which they detected lung cancer smells, BBC News said.

They were successful 71 percent of the time. The researchers showed the dogs were not getting confused by chemicals associated with chronic obstructive pulmonary disease or smoking.

Dr. Thorsten Walles, the report's author from Schillerhoehe Hospital, said, "In the breath of patients with lung cancer, there are likely to be different chemicals to normal breath samples and the dogs' keen sense of smell can detect this difference at an early stage of the disease,” according to BBC News.