"Many of the newer chemotherapy agents are more targeted, although not free from side effects, and can be easier to tolerate than agents typically used 5 to 10 years ago," Greaney says.

But the trend is different for those on long term disability leave due to breast cancer. After rising gradually for several years, the percentage who returned to work leveled off and then fell. In 2001, 47 percent returned to work. That number climbed to a high of 54.8 percent in 2006, then dropped to 50.1 percent by 2009.

"The reasons for this are not entirely clear, but this trend may be influenced by some of the same factors that have improved success in returning to work for people on short term disability," Greaney says. "As treatments become more effective and outcomes improve for many with earlier stage disease, the pool of people who eventually move to long term disability may necessarily be those who have later stage cancer and as a result require more aggressive, debilitating treatments."

Unum says it's important for employers to offer guidance and research to their employees who have to deal with cancer diagnosis and treatment, while helping them return successfully to the workplace.

Cancer is consistently the leading cause of Unum long term disability claims, accounting for about 15 percent of claims each year. Breast cancer is leading type, at about 22 percent of long term disability cancer claims.

Almost 7 percent of Unum short-term disability claims are prompted by cancer, and breast cancer is the leading type at 17 percent of short term disability cancer claims.