Rosen's Breast Pathology, 4e

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Chapter 11

FIG. 11.74.  Invasive duct carcinoma with formation of basal lamina components. The same tu- mor is depicted in all images. A: The carcinoma with an alveolar structure invades fat. There are compressed cells that resemble myoepithelial cells at the perimeter of some of the rounded tumor cell clusters. B: The immunostain for actin reveals reactivity in a small central blood vessel but not in the carcinoma, indicating absence of myoepithelial cells. C: Alveolar nests of carcinoma cells are encircled here by a thin band of laminin reactivity. D: The alveolar groups of carcinoma cells are partially encompassed by reactivity for type IV collagen. Some of the type IV collagen reactivity is associated with small blood vessels in the tumor.

Solin et al. 307 limited the term microinvasion to a “maxi- mal extent of invasion of less than 2 mm or invasive car- cinoma comprising less than 10% of the tumor.” ALN metastases were found in 2 (5%) of 39 patients with micro- invasion. The majority (67%) had comedocarcinoma, but microinvasion was also found in patients with cribriform, papillary, micropapillary, and solid types of DCIS. After a median follow-up of 55 months, one patient (7%) had de- veloped a distant recurrence, and there were nine instances (24%) of local recurrence in the breast after conservation therapy. Silverstein et al. 87 employed the term “microinvasion” if “one or two microscopic foci of possible invasion no more than 1 mm in maximum diameter were found or if the pa- thologists were uncertain as to whether or not a cancerous lobule was tangentially sectioned or infiltrating.” Microin- vasion as so defined was detected in 28 (13%) of 208 cases. The majority of microinvasive lesions were comedocar- cinoma (21 of 28, 75%), representing 20% of intraductal

not separately categorized (notably, micrometastasis in a lymph node is designated as N1mi in the TNM system). When multiple foci of microinvasion are present, there is no agreed-upon method for estimating their aggregate ex- tent, and these cases qualify as DCIS with microinvasion; however, the number of microinvasive foci should be re- ported. Foci of invasion that measure more than 1 mm are diagnosed as invasive ductal carcinoma and reported (and staged) on the basis of the maximal measured extent of invasion.

CLINICAL SIGNIFICANCE OF MICROINVASION

Earlier published reports about microinvasive duct carci- noma had used different definitions of this entity. As a re- sult, comparison of data between these studies must take these differences into consideration.