Lung cancer could be detected by cancer-sniffing dogs said German researchers on Thursday.

A study, published in European Respiratory Journal, indicated that in about 70 percent of cases, the dogs were able to detect tumors.

Researchers tested two German shepherds, an Australian shepherd, and a Labrador retriever, all of them trained to lie down in front of the test tubes where they smelled lung cancer and touch the vial with their noses.

The four dogs could accurately identify cancer in 71 out of 100 samples from lung cancer patients, while ruling out cancer in 372 out of 400 samples that were without cancer, the authors noted.

The surprising result of seven percent false positives points to a very high specificity of trained dogs to identify lung cancer, said study researcher Thorsten Walles, MD, a lung surgeon at Schillerhoehe Hospital in Gerlingen, Germany.

"It even surpasses the combination of chest computed tomography (CT) scan and bronchoscopy, which is an invasive procedure that needs some form of anesthesia," Walles told WebMD. According to Walles, the length of training period could make an important difference between studies on dogs' ability to detect cancer.

In the study, researchers involved dogs to test whether they could correctly smell diseases such as diabetes, bladder cancer, breast cancer and colon cancer. The dogs went through nine months of training for the study, while previous studies used dogs trained only for three weeks.

Over the years, researchers have theorized that cancer has a detectable scent, coming from chemical compounds produced by cancer cells out of the lungs as gas.

"This is probably the most sophisticated study I've seen on this topic," said Dr. Len Lichtenfeld of the American Cancer Society.

CNN reported that the breeds involved in the study included Labrador retriever, German shepherd and Australian shepherd. CNN also reported that Lichtenfeld, deputy chief medical officer, said, "This is probably the most sophisticated study I've seen on this topic. More and more studies are reinforcing the possibility that this is very real."

While the new study is certainly a big step forward, questions still remain, critics remarked.

"We've seen this happen enough to suggest there are compounds in the breath of patients with cancer that could provide an early warning about the presence of cancer in the body, but we still do not know exactly what those compounds are," said Lichtenfeld. "We can't pick out what the dogs smell."

According to Suresh S. Ramalingam, M.D., associate professor and director of the lung program at Emory University's Winship Cancer Institute in Atlanta, because of the varying success rates between dogs and between samples, there needs to be reliable technology that can repeat what dogs do in sniffing out cancer.

"This is the holy grail," Ramalingam told WebMD. "The dogs show that it can be done. We need to find out what the dogs are sniffing so we can do it in a more scientific manner."

According to the American Lung Association (ALA), lung cancer is the second-most common cancer in both sexes and the most common cause of death from cancer.

In 2010, approximately 222,520 new cases of lung cancer were expected to be diagnosed. ALA also reported that more than 80 percent of Americans with lung cancer were older than 60.