A Duke University cancer researcher who resigned in November amid questions about his work has retracted a study in the New England Journal of Medicine. The study reported that a gene profiling test could help show which lung cancer patients most need chemotherapy.

A letter from the scientist, Anil Potti (uh-NEEL' POT'-ee), and his co-authors was published online Wednesday by the journal.

It says that the authors have not been able to reproduce the results they reported in their 2006 study. The letter says they "deeply regret" the effect this has had on other scientists.

Potti resigned amid questions about other research he led, and as the university was looking into whether he had lied on a federal grant application.