WEDNESDAY, March 18 (HealthDay News) -- Early detection of second breast cancers can reduce the risk of death by as much as half, according to an international study.

The researchers looked at information on 1,044 women who were seen at a medical center in Florence, Italy, between 1980 and 2005 and who had developed a second breast cancer -- 455 with cancer in the same breast (ipsilateral) and 589 with cancer in the opposite breast (contralateral). Of the second breast cancers, 67 percent were asymptomatic, and 33 percent were symptomatic.

The study found that chances of survival improved between 27 percent and 47 percent if the second breast cancer was detected in the early, asymptomatic stage rather than at a later stage when women started to experience symptoms.

The researchers also found that mammography was more sensitive than clinical examination for detecting second breast cancers -- 86 percent vs. 57 percent. However, 14 percent of the cancers were detected only by clinical examination.

Asymptomatic cancers were smaller than symptomatic cancers, and early-stage cancers were more common in asymptomatic women (58 percent) than in symptomatic women (23 percent). Fewer women with asymptomatic than symptomatic contralateral cancer had node metastases, an indication the cancer may have spread.

The study was published online March 18 in the Annals of Oncology.

"Our study provides new evidence on several aspects of early detection of second breast cancers," study leader Nehmat Houssami, a breast physician in the School of Public Health at the University of Sydney, Australia, said in a news release from the journal. "We set out to estimate the effect of early, asymptomatic detection while adjusting for the two main biases known to be associated with non-randomized studies of the impact of early detection -- lead time and length bias -- so we believe that the estimates we report are more valid than previously reported estimates, while acknowledging the limitation that the evidence is not from a randomized, controlled trial."

"In addition, we have estimated this for early detection of either ipsilateral or contralateral breast cancer, while other studies have focused on one or the other," Houssami said. "So our estimates may be more useful for clinicians discussing this aspect of breast cancer follow-up with their patient."

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