If you aren’t sure when to start getting colonoscopies andmammograms, just think family history.

According to a multi-institutional study published in the July13 issue of the Journal of the American MedicalAssociation, changes in family history significant enough toalter screening recommendations are common in adults ages 30 to50.

About 22 percent of individuals have a family history thatsuggests familial or hereditary predisposition to cancer, the studyreports. However, little is known about how risk changes over timeand if those changes may qualify patients as candidates for earlieror more intense screening.

Researchers from the National Cancer Institute-funded CancerGenetics Network analyzed both the detailed family historyinformation participants reported upon enrollment in thenetwork—which reflected their cancer risk up until that time—andthe updated information they provided on an annual basis over anaverage of eight years. Analysis focused on colorectal, breast andprostate cancer, because the established screening guidelines forthose common tumors can be affected by family history.

“Clinically relevant family history changes substantially duringearly and middle adulthood, particularly for colorectal and breastcancer, for which the percentage recommended for high-riskscreening increases 1.5- to 3-fold between ages 30 and 50 years,”researchers wrote.

The study found that 2.1 percent of participants at age 30 wouldhave met criteria for colonoscopy screening, with the percentageincreasing to 7.1 percent by age 50 and peaking at 11 percent atage 70.

Findings were similar for breast cancer risk, “with steadyincreases in the percentage of participants who would have metcriteria for MRI screening through early and middle age, from 7.2percent of women at age 30 to 11.4 percent at age 50.”

Although there was an increase in the percentage of men meetingcriteria for early prostate screening, it remained relatively lowcompared to the others, increasing to 2 percent by age 50.