Background: Signet ring cells (SRCs) often accompany gastrointestinal carcinoma, referred to as SRC carcinoma;\nhowever, breast cancers containing SRCs have not been well characterized, leaving the prognostic significance of\nSRCs undetermined. We have described clinicopathological characteristics of patients with breast cancer containing\nSRCs in relation to the expression levels of MUC1, MUC2, MUC4, MUC5AC, and MUC6.\nMethods: Twenty-two breast cancer cases with variable degrees of SRC population were retrospectively studied.\nEach case was categorized as high (>31 %) or low (<30 %) SRC tumor. The SRCs were morphologically classified\ninto the intra-cytoplasmic lumen (ICL) type, or the non-ICL type. The expression levels of MUC1, MUC2, MUC4,\nMUC5AC and MUC6 were determined immunohistochemically. Depending on its subcellular localization, MUC1\nwas categorized as the luminal and cytoplasmic (LC) type, or the cytoplasmic with circumferential membranous\naccentuation (CM) type. These histological findings were compared with other clinicopathological parameters.\nResults: The series consisted of invasive ductal carcinoma (n = 9), invasive lobular carcinoma (n = 9), and mucinous\ncarcinoma (n = 4) cases. The SRC population accounted for 8ââ?¬â??81 % of the tumor cells. Eight cases had ICL type\nSRCs, and the remaining 14 had non-ICL type SRCs. Neither the high (n = 12) and low (n = 10) percentage of SRCs,\nnor the SRC types affected the clinicopathological parameters. In the low MUC1 group (n = 11), larger tumors,\nhigher nuclear grade, lymph node metastasis, and negativity for estrogen receptor was more frequently identified\ncompared to the high MUC1 group (n = 11; p = 0.01, p = 0.002, p = 0.008, and p = 0.02, respectively). The CM group\n(n = 7) had more patients with large-sized tumors, lymph node metastasis, lymphovascular invasion, and higher Ki67\nindices than the LC group (n = 15; p = 0.04, p = 0.001, p = 0.006, and p = 0.03, respectively). The expression levels of\nMUC2, MUC4, MUC5AC, and MUC6 showed no clinicopathological significance. Two patients with low MUC1\nexpression and CM patterns had tumor recurrence, resulting in death, while all the other patients survived without\nrecurrence.\nConclusion: Our results demonstrate that in breast cancers containing SRCs, low MUC1 expression and/or its CM\nsubcellular localization patterns are associated with unfavorable clinicopathological factors. The utility of MUC1\nexpression as a prognostic marker remains to be verified in future studies.
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