Seventeen examples of a variant of @entity513 in situ (DCIS) composed exclusively or predominantly of spindle cells arranged in fascicles, whorls, and solid sheets are described. The fascicular arrangement of the spindle cells simulates the "streaming" phenomenon associated with @entity2543 (IDH). This process also resembles the myoid, solid form of intraductal myoepithelial proliferation. The @entity1 ranged in age from 38 years to 79 years with a mean age of 59.3 years. Five @entity1 presented with a palpable mass. The remaining @entity5 were discovered using mammography. The radiological appearances of the lesions raised concern for @entity189 , but there were no distinctive mammographic findings to suggest an unusual variant of DCIS. Cytological preparations were suspicious for @entity5 in two @entity1 and were reported as malignant in another case. Sixteen @entity1 were treated with wide local excision, and one @entity1 had a partial mastectomy. The @entity5 measured from 3 mm to 15 mm (mean 8.65 mm). In three cases, minute foci of stromal invasion were associated with the spindle cell DCIS. In another specimen, a 2.7-cm @entity513 of no special type was identified in an area away from the foci of the spindle cell DCIS. None of the @entity1 has experienced recurrence or @entity3 during the relatively short mean follow-up period of 16.2 months (range 4-77 months). Spindle cell DCIS is distinguished from the streaming pattern of ordinary IDH by its solid growth pattern, lack of secondary spaces or peripheral fenestrations, uniformity of appearance and distribution of nuclei, cytological atypia in the range of low to intermediate-grade DCIS, and negative immunoreaction with CK-34betaE12 (HMW-CK903). When fenestrations are present, they are evident in areas of cribriform DCIS that merge with the solid, spindle cell areas in hybrid ducts harboring both patterns. This admixture, with conventional cribriform DCIS, and the association with foci of @entity513 in some cases further help recognition and confirmation of this lesion as in situ @entity189 . When there is no transition from the spindle cells to recognizable cribriform DCIS, distinction from @entity1373 (myoepitheliosis) requires immunostains for actin and @entity4483 protein. Recognition of this pattern of DCIS is important in order to avoid its frequent misclassification as a benign lesion.

@entity513 in situ. An unusual variant of @entity5 that simulates XXXX or a myoepithelial proliferation.

@entity1 :: ('9606', 'Species') :: ['women', 'woman', 'patients'] @entity5 :: ('MESH:D009369', 'Disease') :: ['malignancy', 'tumors'] @entity1373 :: ('MESH:D006965', 'Disease') :: ['intraductal myoepithelial hyperplasia'] @entity189 :: ('MESH:D002277', 'Disease') :: ['carcinoma'] @entity4483 :: ('6285', 'Gene') :: ['S-100'] @entity513 :: ('MESH:D044584', 'Disease') :: ['ductal carcinoma', 'invasive ductal carcinoma'] @entity2543 :: ('MESH:D017573', 'Disease') :: ['ordinary intraductal epithelial hyperplasia'] @entity3 :: ('MESH:D009362', 'Disease') :: ['metastasis']
@entity1373 :: (MESH:D006965,Disease) :: ['ductal hyperplasia']
