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BACKGROUND: In this study, the pattern of distribution of the nuclei immunoreactive with Ki67 was examined in DIN1c (DCIS, grade 1/low grade), DIN2 (DCIS, grade 2/intermediate grade), and DIN3 (DCIS, grade 3/high grade). The lesions were evaluated to determine if distinctive patterns could be identified in correlation with lesion grade. METHODS: Fifty seven (n=57) consecutive DIN cases were investigated. Of these, 15 qualified as DIN1c, 28 as DIN2 and 14 as DIN3. The patterns of distribution were recorded for each case as either basal/peripheral or haphazard within the epithelial proliferation. RESULTS: There was a statistically significant difference between the DIN1c, DIN2 and DIN3 in terms of basal/peripheral versus haphazard distribution of Ki67 immunostaining (Chi-square test, P<0.0001). Basal/peripheral staining pattern was dominant among the DIN1c cases, while haphazard staining pattern was the dominant distribution among the DIN3 cases. One half of the DIN2 cases showed basal/peripheral staining pattern, while the other half showed a haphazard staining pattern. CONCLUSION: High grade DIN lesions show haphazard Ki67 staining while low grade DIN lesions show basal/peripheral Ki67 staining in the proliferating epithelial cells. This feature could be practical in separating DIN lesions into low grade (basal/peripheral-Ki67) and high grade (haphazard-Ki67) eliminating the grade 2/intermediate category.

Pathologists should be aware of the existence of a rare CK7-negative variant of breast carcinoma in general, and of Paget's disease in particular. Cytokeratin 7-negative Paget's disease and CK7-negative ductal intraepithelial neoplasia (ductal carcinoma in situ) present a major diagnostic challenge for pathologists since there is limited awareness of their existence. When there is classic Paget's morphology on H&E sections, GATA3 positivity should resolve any doubts about the diagnosis in the setting of a CK7-negative neoplastic cell population.