Eng-Huat Tan, MD, a senior consultant in the medical oncology department at Singapore's National Cancer Center, says his patient, identified as "Mr. S," had been taking the drug Xeloda since July 2005 to prevent recurrence of advanced cancer that had responded well to chemotherapy.

The cancer patient was detained by U.S. Customs officials for four hours in December 2008 because they could not detect fingerprints. The Customs officials later determined that the man was not a security threat.

Tan says people being treated with Xeloda, described as an oral chemotherapy drug, should carry a letter from their doctor that they are taking the medication if they want to travel to countries that require fingerprints for identification.

According to the letter in Annals of Oncology, other cancer patients taking the drug have reported similar side effects.

 "Mr. S" did not know his fingerprints had disappeared, according to Tan.