Data from the women who developed chronic pain was then compared to the women who did not report chronic pain. In addition to age, the women most likely to suffer debilitating chronic pain had more extensive surgery followed by radiation, and reported the most severe pain in the first week after their operation.

Researchers were surprised to find that a woman's anxiety before surgery did not emerge as a direct risk factor for chronic pain, as previous studies had shown that anxiety is clearly a risk factor for acute, post-operative pain.

Most pain stems from damage to the intercostal brachial nerve, which runs under the arm and rib cage. But many other triggers exist as well: scarring, post-operative radiation therapy, some chemotherapy drugs, and the unusual sensations often associated with phantom pain.

Pain is a difficult topic for people with cancer, Dworkin said.

"For some individuals acknowledging pain can be frightening because they think it might mean recurrence or metastasis," Dworkin said. "We've also found that it is difficult for people with cancer to characterize their pain and to report it to their doctors. They are concerned that talking about pain will distract the oncologist from focusing on other aspects of the treatment plan."