Confounding factors make mammography less accurate

Hormone replacement therapy, previous breast surgery, and a low body mass index may reduce the accuracy of screening mammography, according to a study in the August issue of the British Medical Journal.

Age, family history, physical activity levels, smoking, and alcohol consumption did not significantly affect the exam's sensitivity or specificity.

Dr. Emily Banks, deputy director of the cancer research U.K. epidemiology unit at the University of Oxford, and colleagues studied 122,355 women from 50 to 64 years of age. The participants in the U.K.'s Million Women Study had all completed a lifestyle questionnaire and were monitored for 12 months.

The researchers reported an overall sensitivity of 86.6% and specificity of 96.8% for the diagnosis of breast cancer in 726 women.

The following factors had an adverse affect on both sensitivity and specificity:

• Use of hormone replacement therapy: For current, past, and no use, the sensitivity was 83%, 84.7%, and 92.1%, respectively, while specificity was 96.8%, 97.8%, and 98.1%.

• Previous breast surgery versus no surgery: Sensitivity was 83.5% and 89.4%, respectively; specificity was 96.2% and 97.4%.

• Body mass index less than 25 versus greater than or equal to 25: Sensitivity was 85.7% and 91.0%, respectively; specificity was 97.2% and 97.4%.

Women who have these confounding factors also are more likely than other women to have breast cancer diagnosed between screens, Banks said.

While study results indicate that some women may be at a disadvantage in terms of screening mammogram accuracy, the researchers cautioned that it is still the best way to find early stage breast cancers.

They highlighted their results as indicative of the importance of routine screening and of women remaining vigilant between screenings.

For more from the online Diagnostic Imaging archives:

False-positive rate for screening mammography drops

Yearly mammograms prove insufficient for BRCA carriers

MR spectroscopy adds specificity to breast MR

Dutch researchers dismiss HRT link to breast density

Hormone replacement therapy complicates search for cancer