Ductal carcinoma in situ (DCIS) breast specimens need to be embedded completely in order to determine the correct extent of the disease

11061 Background: The processing of breast specimens suspicious of ductal carcinoma in situ (DCIS) is hampered by the fact that DCIS is not regularily visible at the gross level. There is no general consensus as how to process those breast specimens. Suggestions lead from examination of the entire tissue sample with a special focus on the resection margins to algorithms such as cutting only those paraffin blocks containing calcifications. Methods: In order to identify the influence of the diagnostic method on the measured extent of a DCIS lesion we compared two approaches. One was based on the examination of a single section and the other on examination of the entire specimen, i.e. cutting multiple 0.5 cm slices to be analyzed as max. 52 x 76 mm whole mount sections. 187 consecutive breast specimens from 186 patients (median patient age 60 years, range 31 to 87 years) from three gynecological institutions between Jan 2004 and Nov 2006 were searched for DCIS. We compared the largest tumor diameter from a single section of a specimen (‘apparent diameter‘, AD) with a ‘reconstructed diameter‘ RD calculated on the basis of the number of 0.5 cm slices taken from a sample and the number of slices containing the DCIS lesion. Results: Complete histological examination of these 187 cases (90 high and 97 low grade DCIS lesions) revealed a statistically significant difference (p=7.5E-9) between the apparent diameter AD (mean 22.4 mm, range 2 to 80 mm) and the reconstructed diameter RD (mean 31.6 mm, range 6 to 76 mm). In 138 cases (73.8%) the true extent of the disease would have been underestimated (RD > AD) if the diagnosis had been based only on a single exemplary section, the mean difference RD-AD being 14.8 mm (range 1–50 mm). In addition, we found 40 invasive cancers (multifocal inside the DCIS lesion, unifocal inside the DCIS and unifocal outside the DCIS). Conclusions: We conclude that the complete examination of a breast specimen helps to determine the true extent of DCIS and additionally helps to identify cases that turn out to be already invasive. Both findings may have important impact on the patients’ further treatment and outcome. No significant financial relationships to disclose.