The reversed apical pattern of MUC1 expression is characteristics of invasive micropapillary carcinoma of the breast.
BACKGROUND
Invasive micropapillary carcinoma (IMPC) of the breast is a special subtype of invasive ductal carcinoma (IDC), which is known to have a high potential to metastasize to the axillary lymph node. However, it is sometimes difficult to differentiate IMPC from conventional IDC showing an IMPC-like pattern due to artifact (pseudo-IMPC). In the present study, we investigated the usefulness of immunohistochemical expression of MUC1 for distinguishing IMPC from pseudo-IMPC, and analyzed several clinicopathological parameters of IMPC and pseudo-IMPC cases.


METHODS
Eighty cases showing IMPC or IMPC-like pattern were selected from our surgical files of 1,240 cases of IDC. We examined the expression of MUC1, D2-40 and CD34 by immunohistochemistry.


RESULTS
Eighty cases were classified into 9 cases (0.7%) of pure-IMPC, 31 cases (2.5%) of mixed-IMPC, and 40 cases of pseudo-IMPC, according to the expression pattern of MUC1. In pure-IMPC cases, MUC1 expression was found at the reversed apical membrane of neoplastic cell clusters, while in pseudo-IMPC, MUC1 expression was present in the whole cytoplasmic membrane and/or cytoplasm. There were no significant differences among the three groups in patient age, tumor size and nuclear grade of neoplastic cells. However, lymphatic invasion and lymph node metastasis in the pure-IMPC or mixed-IMPC cases were higher than those in pseudo-IMPC cases with statistically significant values. Pure-IMPC has a higher recurrence rate and lower overall survival compared to pseudo-IMPC [P = 0.0165(DFS) P = 0.025(OS)].


CONCLUSIONS
This study demonstrated that immunohistochemistry of MUC1 is useful for the diagnosis of IMPC. The pure-IMPC cases had higher incidences of lymphatic invasion and lymph node metastasis, and also showed a poorer prognosis.
Li
Yu-sang
YS
Department of Pathology, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima 734-8551, Japan.
Kaneko
Mayumi
M
Sakamoto
Danielle Giacometti
DG
Takeshima
Yukio
Y
Inai
Kouki
K
D000951:Antigens, Neoplasm; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D018270:Carcinoma, Ductal, Breast / Q000378:metabolism* / Q000556:secondary; D002291:Carcinoma, Papillary / Q000378:metabolism* / Q000556:secondary; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D008207:Lymphatic Metastasis; D008875:Middle Aged; D018396:Mucin-1; D009077:Mucins / Q000378:metabolism*; D009361:Neoplasm Invasiveness; D011379:Prognosis; D015996:Survival Rate
D000951:Antigens, Neoplasm; C060192:MUC1 protein, human; D018396:Mucin-1; D009077:Mucins