When considering at what intervals to be screened for breast cancer, women and their doctors may have another insight to take into account:

Which side of menopause you’re on could be more important than how old you are.

The study behind this suggestion posted in JAMA Oncology Oct. 20, the same day the American Cancer Society bumped its recommendation on the starting age for screening from 40 to 45 for women at average risk. The change drew from an evidence review led by the ACS and published that day in JAMA.

In the JAMA Oncology study, Diana Miglioretti, PhD, of UC-Davis and colleagues examined the roles played by age, menopausal status and postmenopausal hormone therapy.

They looked at these factors while comparing tumor characteristics in more than 15,400 women with breast cancer, ranging in age from 40 to 85, who had annual vs. biennial screening mammograms.

They found that premenopausal women diagnosed with breast cancer following a biennial screening mammogram were more likely to have larger, more advanced tumors than women screened annually.

Meanwhile, postmenopausal women not receiving hormone therapy had a similar proportion of tumors with less favorable prognostic characteristics—primarily defined as stage IIB or higher—regardless of whether their screening mammogram was biennial or annual.

Most of the women were 50 or older (13,182 or 85.4 percent), white (12,063 or 78.1 percent) and postmenopausal (9,823 or 63.6 percent).

Premenopausal women (2,027 or 13.1 percent) had higher proportions of ductal carcinoma in situ (DCIS) vs. invasive cancers and invasive tumors with less favorable prognostic characteristics than postmenopausal women.

Among premenopausal women, women screened biennially vs. annually had:

• A higher proportion of stage IIB or higher tumors (25.7 percent vs. 19.8 percent);
• Tumors greater than 15 millimeters (65.3 percent vs. 54.6 percent); and
• Node-positive disease (36.6 percent vs. 31.3 percent).

The researchers did not measure breast cancer mortality.

In their study discussion, Miglioretti et al. note that tumors exposed to estrogen “may grow faster, decreasing the detectable preclinical phase and resulting in a higher proportion of interval cancers with poorer tumor characteristics. In addition, breast density decreases after menopause, making it easier to diagnose breast cancers when they are smaller.”

If screening guidelines were based on menopausal status rather than age, they add, “some women ages 40 to 54 years might be recommended for more frequent screening and others, less frequent screening.”

JAMA Oncology published an accompanying opinion piece by Wendy Chen, MD, MPH, of Brigham and Women’s Hospital in Boston.

“This study and others have clearly demonstrated that with less frequent mammography, the tumors will be bigger and have a slightly more advanced stage,” writes Chen. “However, with our better understanding of tumor biology and improvements in targeted therapy, the best way to optimize the risk and/or benefit of screening may not be to maximize the chances of finding a smaller tumor.”

Chen recommends taking a different tack.

Forthcoming research, she writes, should focus on gaining “a better understanding of how screening interacts with tumor biology” in order to better grasp differences between “the types of interval cancers and sojourn times and how these characteristics differ by age and/or menopausal status.”