DUBLIN - Persistent hiccupping in addition to weight-loss and difficulty swallowing could be a warning sign of cancer of the esophagus, an Irish researcher said on Wednesday.

Professor Tom Walsh, of the James Connolly Memorial Hospital in Dublin, told a meeting of the Royal College of Surgeons in Ireland that some patients with esophageal cancer complain of persistent hiccups.

"Up to now, hiccups have not been recognized as a possible harbinger of cancer," Walsh told Reuters.

But in a study of 99 patients with the disease he said 27 percent complained of persistent hiccups and six percent said it prompted them to see a doctor.

Hiccups are caused by the involuntary spasm of the diaphragm which causes the vocal cords to close very briefly. Eating too quickly or too much, coughing, laughing and too much alcohol are thought to cause hiccups.

Swallowing and breathing into a paper bag are remedies that are used to cure hiccups.

Walsh believes hiccups in cancer patients could be linked to the phrenic nerve, the motor nerve of the diaphragm.

"Nobody knows why, but there may be the involvement of the vagus nerve or the phrenic nerve," he said.

Nine percent of the patients in the study described hiccupping as the predominant ongoing symptom.

Oesophageal cancer is the sixth most common cancer worldwide with more than 400,000 cases detected each year, according to the International Agency for Research on Cancer in France.

Most cases are detected when the disease is in an advanced stage. Smoking and alcohol are the most important risk factors.