A US man, who was being treated for prostate cancer, developed an uncontrollable 'Irish brogue' accent, despite having no Irish background.

Researchers in the US said the development was consistent with Foreign Accent Syndrome (FAS).

According to a study, published in the British Medical Journal, the man, who was in his 50s, was diagnosed with small cell neuroendocrine prostate cancer and was receiving treatment.

His 'Irish brogue' accent was uncontrollable, present in all settings and gradually became persistent.

The man had lived in England when he was in his 20s and had friends and distant family members from Ireland, but he had never been to Ireland and had never spoken with an Irish accent.

"He had no neurological examination abnormalities, psychiatric history or MRI of the brain abnormalities, at symptom onset", according to the study, which was jointly done by researchers from North Carolina's Duke University and the Carolina Urologic Research Center of South Carolina.

Despite chemotherapy, his cancer progressed resulting in brain metastases and paralysis, leading to his death.

Doctors found that the most likely cause of the speech change was due to a so-called paraneoplastic neurological disorder, which developed as his immune system fought the cancer.

The research team said the case study improves the minimal literature on Foreign Accent Syndrome.

It is understood to be the first case of FAS in a patient with prostate cancer and the third such case in someone with a malignancy.

Limited details about the man have been published, due to patient confidentiality.