James R. Young, chairman, president, and CEO of Union Pacific Corp. (UP), has been diagnosed with pancreatic cancer and will take a medical leave of absence from his president and CEO duties to undergo treatment, the company said today. He will remain as chairman, the Omaha, Neb.-based company said.

UP has named John J. Koraleski, executive vice president-marketing and sales, to serve as acting president and CEO during Young's absence. Koraleski is a 40-year veteran of UP.

Young, 59, joined UP in 1978. He was named president and CEO of the parent company in 2005 and chairman in 2007. Prior to 2005, he was president and COO of Union Pacific Railroad, a position he was elected to in January 2004.

News of Young's illness and departure comes as UP enjoys perhaps the greatest financial streak in its 150-year history. Earlier this year, the company reported 2011 results that set all-time annual records for net and operating income. Its fourth quarter 2011 results set all-time quarterly records for both net and operating income, the company said.

The original Union Pacific was formed on July 1, 1862, when President Abraham Lincoln signed the Pacific Railway Act.