Inflammatory breast carcinoma (IBC) is characterized by florid tumor emboli within lymphovascular spaces termed lymphovascular invasion (LVI). Using a human-scid model of IBC (MARY-X), we have demonstrated using retrovirally-mediated dominant-negative E-cadherin mutant approaches (H-2K(d)-E-cad), that the tumor cell embolus (IBC spheroid) forms on the basis of an intact and overexpressed E-cadherin/alpha, beta-catenin axis which mediates tumor cell-tumor cell adhesion analogous to the embryonic blastocyst and accounts for the compactness of the embolus. The tumor cell embolus (IBC spheroid), in contrast, fails to bind the surrounding vascular endothelial cells both in vitro and in vivo because of markedly decreased sialyl-Lewis X/A carbohydrate ligand-binding epitopes on its overexpressed MUC1 which are necessary for binding endothelial cell E-selectin. This tumor cell-endothelial cell aversion further contributes to the compactness of the IBC spheroid and its passivity in metastasis dissemination. This passivity is manifested by a dramatic increase in metastatic pulmonary emboli following palpation of the primary tumor. In assessing this passivity of metastatic dissemination, we compared the effects of palpation on MARY-X with the effects of palpation on a derived dominant-negative E-cadherin mutant (H-2K(d)-E-cad), as well as other well known human tumoral xenografts exhibiting no (MCF-7, T47D), low (MDA-MB-231, MDA-MB-468) or high (C8161, M24(met)) levels of spontaneous metastasis but no LVI. Palpation of each xenograft similarly increased intratumoral pressure by 200% (10-->30 mmHg) but dramatically increased the numbers and sizes of pulmonary metastases 10-100-fold (P<0.001) only in MARY-X. The mechanism of this effect was through an immediate post-palpation release of circulating tumor emboli detected 2-3 min after palpation (P<0.01) by human cytokeratin 19 RT-PCR of extracted RNA from 300 microl of murine blood. Although circulating human tumor cell-derived growth factors (IGF-I, IGF-II, TGF-alpha and TGF-beta) and angiogenic factors (VEGF and bFGF) were detected by ELISA in murine serum of MARY-X, palpation did not further increase the circulating levels of these factors (P>0.1). Our findings support the cooperative role of E-cadherin and sialyl-Lewis X/A-deficient MUC1 in the passive dissemination of tumor emboli in IBC.