33 Special Types of Invasive Breast Carcinoma: Diagnostic Criteria ...

These atypical vascular lesions have, thus far, proven to follow a benign course.
Finally, I would like to point out that unusual cases of ductal carcinoma in situ have a
large population of spindle cells that is 10% to 80% of the in-situ tumour cell
population in one report (162). Although this would not cause a diagnostic problem in
an excision biopsy, it could cause trouble in a limited needle biopsy or fine needle
aspiration biopsy, where the spindle cells could be confused with other spindle-cell
lesions. Almost all DCIS lesions with spindle cells disclose neuroendocrine
differentiation. Although the distinction from benign florid usual hyperplasia may
pose a diagnostic histological problem in an excision biopsy specimen, the presence of
diffuse neuroendocrine expression, in conjunction with the pattern of high molecular
weight keratin profile (CK5/6 negative) on immunohistochemistry, supports an in-situ
neoplastic process. The absence of smooth-muscle acitin immunostaining, in
conjunction with negative reactivity for cytokeratins 5/6 and 14, makes the possibility
of a myoepithelial proliferation unlikely.
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