Introduction of mammography screening may increase breast surgery rates

Mammography screening may increase rates of breast surgery, including mastectomy, according to a new study.

Norwegian researchers performed a comparative analysis from a national cancer registry to determine whether the introduction of mammography screening throughout the country affected rates of surgical breast cancer treatment. In Norway, mammography screening for women age 50 to 69 years began in four counties in 1996 and was introduced into the remaining 15 counties sequentially between 1999 and 2004.

Population-based data were examined from 1993 to 2008 for women 40 to 79 years of age who underwent surgical treatment for invasive breast cancer or ductal carcinoma in situ. The study's main outcome measures were rates of breast surgery, defined as mastectomy plus breast-conserving treatment, and rates of mastectomy alone for women age 40 to 49 years, 50 to 69 years, and 70 to 79 years. The authors also calculated changes in rates of breast surgery between 1993-1995 (prescreening), 1996-2004 (introduction of screening), and 2005-2008 (screening) in women who were invited to screening and those who were not. The study results were published online Sept. 13 by BMJ.

From the prescreening to the screening period, the annual breast surgery rate in the invited age group (50 to 69 years) increased from 180 to 305 per 100,000 women (hazard ratio, 1.70; 95% CI, 1.62 to 1.78). In younger noninvited women (age 40 to 49 years), the increase was smaller, from 133 to 144 per 100,000 women yearly (hazard ratio, 1.08; 95% CI, 1.00 to 1.16), and in older noninvited women (age 70 to 79 years), the rate decreased from 227 to 214 per 100,000 women yearly (hazard ratio, 0.92; 95% CI, 0.86 to 1.00).

Rates of mastectomy alone decreased between the prescreening and screening periods in invited and noninvited women but increased from 156 per 100,000 women in the prescreening period to 167 per 100,000 women in the introduction of screening period among those 50 to 69 years of age (hazard ratio, 1.09; 95% CI, 1.03 to 1.14). In younger noninvited women over this same period, mastectomy rates decreased from 109 to 91 per 100,000 women annually (hazard ratio, 0.83; 95% CI, 0.78 to 0.90). Women in the invited group had a 31% higher mastectomy rate than those in the noninvited younger group (hazard ratio, 1.31; 95% CI, 1.20 to 1.43).

The authors acknowledged that their study could not adjust for factors other than introduction of mammography screening, such as tumor stage and size, and that choice of surgery may have been influenced by geographic differences. However, they concluded that in Norwegian women age 50 to 69 years, increased rates of both breast cancer surgery and mastectomy alone were associated with mammography screening.

Although mastectomy rates in Norway have recently decreased because of changes in surgical policy, they wrote, these decreases have mainly been seen in unscreened age groups. “A potential benefit of mammography screening—a reduction in mastectomy rates and an increase [in] the use of less invasive surgery—was not corroborated by our results,” the authors wrote.