Sniffer dogs could be the secret weapon for reliably detecting lung cancer, according to German researchers.

The report published in the European Respiratory Journal states that dogs can be trained to detect lung cancer by sniffing human breath. The researchers found that trained dogs could detect a tumor in 71 percent of patients.

WebMD reports that in its early stage, lung cancer has few symptoms, which makes it difficult for doctors to make early diagnosis, when it's still treatable.

This is the holy grail, says Dr. Suresh S. Ramalingam, an associate professor and director of the lung program at Emory University's Winship Cancer Institute in Atlanta, to WebMD. The whole field is focused on using something that's readily available that does not involve an expensive surgery or scan that would allow us to find early cancers.

Ramalingam is developing technology that aims to replicate the ability of dogs to smell trace amount of chemicals produced by cancerous tumors. He's not involved in the research, WebMD states.

Researchers trained four dogs ? two German shepherds, an Australian shepherd, and a Labrador retriever - who accurately identified cancer in 71 of 100 samples from lung cancer patients. The dogs also ruled out cancer in 372 out of 400 samples that were known not to have cancer, giving them a very low rate of false positives, about 7 percent, WebMD states.

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, Dr. Thorsten Walles, lead author from Schillerhoehe Hospital, told BBC. Our results confirm the presence of a stable marker for lung cancer. This is a big step forward.