This study demonstrates decreasing accuracy of mammographic prediction of disease extent with increasing dimension of microcalcification. In particular, DCIS extent was underestimated by an average of 6.75mm (p=0.049) in the 39.6% of patients selected for treatment with WLE who required a second operation. Involved margins and the requirement for a second operation were significantly more frequent in patients with ER negative disease.
Current literature has focused mainly on the effect of ER status on disease recurrence in DCIS18,19
and indications for adjuvant hormonal therapy20
but few studies have commented specifically on its effect on accurately predicting the extent of high-grade DCIS preoperatively. Results from the Sloane Project demonstrated that lesion size has a strong effect on the radiological features of calcified DCIS. However, this study did not comment on the effect of ER status.21
Further research into the importance of ER status is required to ascertain its effect on accurate diagnosis of disease extent and subsequent achievement of adequate surgical margins. ER status could potentially help in the identification of cases likely to harbour mammographically occult, uncalcified disease. This is biologically plausible since the chemical composition of microcalcification differs between DCIS and differing grades of breast cancer.22
These results show that mammography appears to underestimate the size of DCIS by ≥10mm (29%) more frequently than overestimating it in cases selected for treatment with WLE. Similarly, studies by Coombs et al23
and Chakrabarti et al5
have reported a higher incidence of underestimation (15% and 17% respectively) in patients undergoing WLE. The Association of Breast Surgery audit indicated that 23% of B5a (non-invasive) cancers required a second operation after WLE1
and, consistent with this, the overall rate of re-excision of pure DCIS of all grades within our unit was 23% between 2008 and 2009. This is to be compared with a much higher re-excision rate of 39% in this study in the subset of patients with pure-high grade DCIS. Since we specifically selected patients with high-grade DCIS, this higher re-excision rate is interesting and implies increased difficulty in successful management of high grade lesions at first operation. Uncalcified DCIS could be a possible explanation for cases where disease extent was underestimated. Holland and Hendriks outlined the prevalence of uncalcified DCIS, stating that after pathological specimen analysis of 119 cases, DCIS does not generally form a multicentric distribution, ie if two separate areas of microcalcification are seen, the probability of uncalcified disease between these areas is high.24
The number of patients requiring re-excision (n=34) was lower than the number of cases identified as having involved/uncertain margins (n=46). Involvement of DCIS at deep or superficial surgical margins may be less likely to lead to re-excision than at circumferential margins as no further breast tissue can be resected from these margins and it may explain why some patients with positive margins had no further surgery.
It has been reported that greater breast density is related to an increased incidence of associated invasive disease in DCIS25
as dense rather than fatty mammographic parenchymal density surrounding a lesion is more likely to obscure a potential soft tissue abnormality associated with invasive disease. However, the BI-RADS® breast density score was not a significant predictor for invasive disease. Greater extent of microcalcifications on mammography was also not a significant predictor of invasive disease. This corresponds with findings by Stomper et al
where lesions greater than 10mm showed no correlation with greater incidence of invasion. However, other studies have shown an increased risk of invasive disease with more extensive mammographic microcalcifications,27,28
leading to recommendations that staging of the axilla should be performed in these cases. No other significant predictors for invasive disease were identified.
It has emerged that the use of breast magnetic resonance imaging (MRI) could improve the diagnosis of DCIS. An observational study by Kuhl et al
found that 48% of high-grade DCIS lesions diagnosed by MRI were missed by mammography.29
MRI may offer improved diagnosis for patients with areas of uncalcified high-grade DCIS that is otherwise mammographically occult. The current literature suggests MRI is effective for detection of high-grade DCIS but more research is needed to determine whether it provides greater accuracy in predicting disease extent since we demonstrate here that mammography is less accurate at predicting extent of DCIS in larger (>25mm), ER negative lesions, which may be due to uncalcified disease.