Dimorphic variant of ductal carcinoma in situ of the breast

We report a case of dimorphic variant of ductal carcinoma in situ (dimorphic DCIS), composed of an epithelium intermixed with columnar cells and dimorphic cells. The findings of typical DCIS architecture support categorization as DCIS on a low-power view. Furthermore, there was no difference in the nuclear morphology of the two cell types on the high-power view. The two cell types comprising dimorphic DCIS were negative for p63, CK 5/6 and 14. On the contrary, both cell types were diffusely positive for nuclear ER and AR, as well as marked membrane-associated staining for E-cadherin and cytoplasmic staining for GCDFP-15. These immunohistochemical marker results are similar to conventional DCIS and there were no differences in expression patterns between the columnar epithelial cells and dimorphic cells. The morphological features of dimorphic cells may be confused with cells of other origins if the features of dimorphic DCIS are not recognized. Careful observation of morphological architecture and expression of immunohistochemical markers may support diagnosis.