Invasive Micropapillary Carcinoma of the Breast: An Update

Abstract

Context.-Invasive micropapillary carcinoma (IMPC) is a distinct variant of mammary carcinoma in which tumor cells are arranged in morulelike clusters devoid of fibrovascular cores and situated within empty stromal spaces. Identification of IMPC can be achieved by the assessment of morphologic features in conjunction with the characteristic ''inside-out'' staining pattern of epithelial membrane antigen and sialyl Lewis X highlighted by immunohistochemical analysis. Although recognizing micropapillary architecture is often not challenging, the criteria for distinguishing between mixed and pure IMPC remain imprecise. Some mucin-producing carcinomas can also have micropapillary histology, but there is no consensus on whether these tumors are variants of IMPC or mucinous carcinomas. The molecular genetic studies demonstrate that IMPCs have distinct molecular genetic profiles, supporting the theory that they constitute distinct pathologic entities. However, genomic analyses have not identified any specific genomic aberration that may explain the distinctive morphology and clinical behavior of IMPC.Objective.-To provide an overview on the current concepts in the diagnosis and pathogenesis of IMPC of the breast, incorporating recent molecular genetic advances and prognosis-based reclassification.Data Sources.-PubMed search and the cited references were reviewed.Conclusions.-The recent evolution of prognosis-based reclassification and molecular genetic advances has enhanced our knowledge of the pathogenesis of IMPC of the breast. Additional studies might reveal consistent molecular alterations that underlie the formation of the inside-out growth pattern, and they might elucidate the molecular mechanisms responsible for the unfavorable clinical behavior of IMPC.

Prognostic Significance of a Micropapillary Pattern in Pure Mucinous Carcinoma of the Breast: Comparative Analysis with Micropapillary Carcinoma

“…Only cases with tumors containing a ≥90% mucinous component were defined as mucinous carcinoma. Morphologically, micropapillae were defined as clusters of tumor cells separated from surrounding stroma by clear spaces and that exhibited reverse polarity, also known as an “inside-out” growth pattern, whereby the apical pole of the cells faces the stroma rather than the luminal surface [19]. MUMPC was defined as a tumor in which micropapillary features constituted >50% of the tumor epithelial components (Fig.…”

Tumor Budding, Micropapillary Pattern, and Polyploidy Giant Cancer Cells in Colorectal Cancer: Current Status and Future Prospects

“…Micropapillary pattern has been detected in about 20% of CRCs, a phenomenon analogous to the more familiar one seen in some carcinomas of breast, bladder, lung, pancreas, ovary, urothelial tract, and stomach [85–88]. Micropapillary pattern in carcinomas is associated with a greater frequency of lymphovascular invasion and lymph node metastases and poor prognosis [89].…”

Papillotubular carcinoma with an invasive micropapillary carcinoma component of the breast, characterized by a rapid increase in size due to intra-tumoral hemorrhage: A case report

“…Pathologically, a pure IMPC is rare, and the amount of micropapillary architecture in a tumor required for the diagnosis of IMPC has not yet been well established [9]. The 2003 World Health Organization classification of breast tumors listed IMPC as a subtype of invasive carcinoma; however, no specific percentage of the IMPC component within the breast tumor has been proposed as a criterion for the IMPC diagnosis [6], [10].…”

“…Generally, ER and PgR positive status is associated with an improved differentiation of tumors and improved clinical outcome [9]. HER2 over-expression is known to have a poor prognosis in breast tumors [12].…”

“…HER2 over-expression is known to have a poor prognosis in breast tumors [12]. Although IMPC has an aggressive behavior, many studies have reported that IMPC is characterized by higher rates of ER and PgR expression compared to other breast cancer types [6], [7], [8], [9], [10]. However, this is controversial as other reports have mentioned a low rate of ER expression in IMPC [13].…”