Missing breast screening exams raises mortality risk

By Kate Madden Yee, AuntMinnie.com staff writer

March 31, 2015 -- Missing mammography screening exams increases mortality among screening-age women, according to a new study published in the April issue of the American Journal of Roentgenology. Wisconsin researchers found that missing two exams doubles the risk of all-cause mortality, and risk rises with the number of missed exams.

The findings add fuel to the ongoing debate over whether the benefits of mammography screening outweigh its harms -- namely, overdiagnosis and treatment of clinically insignificant cancers, radiation exposure, and anxiety about false positives, wrote study co-author Dr. Adedayo Onitilo, from the Marshfield Clinic Weston Center in Weston, WI, and colleagues.

The new findings are also consistent with earlier research conducted by Dr. László Tabár of Falun Central Hospital in Sweden, which found a 19% decrease in all-cause mortality and a 31% reduction in breast cancer-specific mortality among breast cancer patients who underwent regular mammography (Journal of Medical Screening, December 2002, Vol. 9:4, pp. 159-162).

"Similar to the findings reported by Tabár et al more than a decade ago, the results of the current study show decreased all-cause mortality in breast cancer patients who underwent routine mammography before diagnosis compared with those with missed annual mammography examinations," Onitilo's group wrote. "This significant difference persisted when the data were controlled for age, insurance status, the number of medical encounters, comorbidity status, a family history of breast cancer, and the calendar year."

For their study, Onitilo and colleagues identified primary breast cancer cases diagnosed in the Marshfield Clinic Health System from 2002 through 2008, noting whether annual mammography examinations had been performed in the five years before diagnosis. The final study cohort included 1,421 women with breast cancer, most of which was early stage (85%). Median age at diagnosis was 62 years (AJR, April 2015, Vol. 204:4, pp. 898-902).

Women who had missed any of the previous five annual mammography examinations had a 2.3-fold increased risk of all-cause mortality, compared with subjects with no missed mammography examinations, the researchers found. In fact, there was a progressive increase in risk as the number of missed annual mammography exams increased. The hazard ratio became statistically significant at two annual missed mammography exams.

Increased mortality by No. of missed screening exams
No. of annual mammo exams missed Hazard ratio p-value
1 1.37 0.2052
2 1.97 0.0096
3 2.07 0.0061
4 2.15 0.0033
5 3.55 < 0.0001

"There was definitely a progressive decline in survival," Onitilo told AuntMinnie.com.

Mammography screening is intended to detect breast cancer at an earlier, easier-to-treat stage, the authors noted. Recent studies, including one conducted in 2013 by Onitilo and colleagues, have shown that missed opportunities for screening mammography increase a woman's risk of being diagnosed with breast cancer at a later disease stage (AJR, November 2013, Vol. 201:5, pp. 1057-1063).

"The debate over mammography screening continues, and this one study is not going to resolve it," Onitilo told AuntMinnie.com. "But it does further confirm that mammography is important to women's health, and that women should be screened annually -- at least until we are able to accurately identify women who don't need it each year."


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