Digital mammography finds more small, invasive breast cancers, but it also identifies more ductal carcinoma in situ (DCIS) -- some of which may never cause harm if undetected. But a new study in the April issue of Radiology claims that digital mammography tends to find DCIS lesions that are more likely to progress to cancer.
The findings address one of the concerns about screening mammography: that its high rate of detecting DCIS may contribute to overdiagnosis, or the detection of cancers that would never threaten the life of a woman, German researchers wrote.
Dr. Stefanie Weigel from University Hospital Muenster."Critics of digital breast screening suspect that the high detection rates of lesions depicted as calcifications may enhance overdiagnosis due to an increased detection of DCIS that would never present clinically in a person's lifetime," wrote lead author Dr. Stefanie Weigel, from University Hospital Muenster, and colleagues. "Our results show that, in population-based digital mammography screening, increments of total DCIS detection rates were significantly correlated with detection rates of intermediate- and high-grade DCIS."
DCIS is classified as low-, intermediate-, and high-grade disease, with the interval between DCIS and invasive cancer described as shorter for high-grade lesions (on average, five years) than for low-grade lesions (on average, more than 15 years). Weigel's group sought to investigate the relationship between overall DCIS detection and the specific detection rates of each grade (Radiology, April 2014, Vol. 271:1, pp. 38-44).
The study included breast cancer cases from the German state of North Rhine-Westphalia identified from initial screening exams conducted from October 2005 through December 2008. The cohort contained all screening-detected breast cancers, including the specification of invasive cancer or DCIS and the nuclear grade of each pure DCIS case.
A total of 740,726 women were screened with digital mammography; 6,172 were identified as having screen-detected cancer. Of these, 5,082 (82.3%) were invasive cancers and 1,090 (17.7%) were in situ lesions. Among the in situ lesions, 1,074 were categorized as DCIS and 16 as lobular carcinoma.
Regarding grade, 185 (17.2%) of the 1,074 DCIS were considered low grade, 401 (37.3%) were intermediate grade, and 432 (40.2%) were high grade; grading was missing in 56 cases (5.2%). The average detection rate of all grades of DCIS was 0.14 per 100 women screened. The detection rate of low-grade DCIS was less than the rates for intermediate- and high-grade DCIS.
"The proportion of low-grade DCIS was consistently lower than that of intermediate- and high-grade DCIS," Weigel and colleagues wrote.
All DCIS grades have the potential to progress and become invasive, but low-grade lesions tend to develop more slowly and may not cause harm in a person's lifetime, according to Weigel. Therefore, it's important to determine the proportionate frequency of low-grade DCIS -- at least to get a clearer picture of screening mammography's harms, she said.
"Our work indicates that overdiagnosis due to more detection of very slowly progressive DCIS is less of a problem than frequently suspected," she told AuntMinnie.com via email.
