April 23 (HealthDay News) -- The risk of developing primary or secondary cancer is dependent on the interaction of genetics, personal habits and environmental exposure, new research suggests.

The studies were expected to be presented Monday at the annual meeting of the American Association for Cancer Research, in Los Angeles.

A study by U.S. and Australian researchers found that for women who start having children later in life, breast-feeding may help protect against estrogen and progesterone receptor positive (ERPR-positive) and ERPR-negative breast cancers.

The findings from the study of almost 2,500 women suggest that women who delay having children after age 25 should consider breast-feeding when they do have children, the researchers said.

Another study found that cervical cancer survivors have a 30 percent higher incidence of second cancers than women in the general population. The study looked at 104,760 cervical cancer survivors in Denmark, Finland, Sweden, Norway and the United States who were tracked for 40 or more years after their initial diagnosis of invasive cervical cancer.

The findings suggest that cervical cancer survivors need to be closely monitored for second cancers, the researchers said.

A third study found that genetic instability may help predict which Hodgkin's disease survivors are at greatest risk for second cancers.

Between 1986 and 1992, researchers at the University of Texas M.D. Anderson Cancer Center in Houston analyzed chromosomal abnormalities in lymphocytes from 252 adults Hodgkin's disease patients before they underwent treatment. The researchers looked at the number of chromatid breaks during 100 complete cell metaphases.

The researchers followed the patients for an average of 13 years, and found a strong correlation between the number of chromatid breaks and the risk of developing a second cancer. The 25 percent of patients with the highest number of breaks were nearly two-and-a-half times more likely to develop second cancers.

The findings could prove useful in designing treatment regimens and follow-up surveillance for individual patients, the researchers said.

Another study found that survivors of childhood leukemia and lymphoma have a higher-than-average risk of developing a different type of cancer later in life. An international team of researchers analyzed 13 cancer registries in several countries and found that the cumulative incidence of second cancer was: 2.43 percent, 12.7 percent, and 2.5 percent within 30 years for survivors of leukemia, Hodgkin's lymphoma and Non-Hodgkin's lymphoma, respectively.

The findings show that survivors of these childhood cancers are at "high risk" for developing second cancers later in life, the researchers said.