Metastasis is a complex, multistep process of cancer progression that has few treatment options. A critical event is the invasion of cancer cells into blood vessels (intravasation), through which cancer cells disseminate to distant organs. Breast cancer cells with increased abundance of Mena [an epidermal growth factor (EGF)–responsive cell migration protein] are present with macrophages at sites of intravasation, called TMEM sites (for tumor microenvironment of metastasis), in patient tumor samples. Furthermore, the density of these intravasation sites correlates with metastatic risk in patients. We found that intravasation of breast cancer cells may be prevented by blocking the signaling between cancer cells and macrophages. We obtained invasive breast ductal carcinoma cells of various subtypes by fine-needle aspiration (FNA) biopsies from patients and found that, in an in vitro transendothelial migration assay, cells that migrated through a layer of human endothelial cells were enriched for the transcript encoding MenaINV, an invasive isoform of Mena. This enhanced transendothelial migration required macrophages and occurred with all of the breast cancer subtypes. Using mouse macrophages and the human cancer cells from the FNAs, we identified paracrine and autocrine activation of colony-stimulating factor-1 receptor (CSF-1R). The paracrine or autocrine nature of the signal depended on the breast cancer cell subtype. Knocking down MenaINV or adding an antibody that blocks CSF-1R function prevented transendothelial migration. Our findings indicate that MenaINV and TMEM frequency are correlated prognostic markers and CSF-1 and MenaINV may be therapeutic targets to prevent metastasis of multiple breast cancer subtypes.

Mena, an actin regulatory protein, functions at the convergence of motility pathways that drive breast cancer cell invasion and migration in vivo. The tumor microenvironment spontaneously induces both increased expression of the MenaINV and decreased expression of Mena11a isoforms in invasive and migratory tumor cells. Tumor cells with this Mena expression pattern participate with macrophages in migration and intravasation in mouse mammary tumors in vivo. Consistent with these findings, anatomical sites containing tumor cells with high levels of Mena expression associated with perivascular macrophages were identified in human invasive ductal breast carcinomas and called TMEM. The number of TMEM sites positively correlated with the development of distant metastasis in humans. Here we demonstrate that mouse mammary tumors generated from EGFP-MenaINV expressing tumor cells are significantly less cohesive and have discontinuous cell-cell contacts compared to Mena11a xenografts. Using the mouse PyMT model we show that metastatic mammary tumors express 8.7 fold more total Mena and 7.5 fold more MenaINV mRNA than early non-metastatic ones. Furthermore, MenaINV expression in fine needle aspiration biopsy (FNA) samples of human invasive ductal carcinomas correlate with TMEM score while Mena11a does not. These results suggest that MenaINV is the isoform associated with breast cancer cell discohesion, invasion and intravasation in mice and in humans. They also imply that MenaINV expression and TMEM score measure related aspects of a common tumor cell dissemination mechanism and provide new insight into metastatic risk.

Cancer stem cells (CSCs) play an important role during metastasis, but the dynamic behavior and induction mechanisms of CSCs are not well understood. Here, we employ high-resolution intravital microscopy using a CSC biosensor to directly observe CSCs in live mice with mammary tumors. CSCs display the slow-migratory, invadopod-rich phenotype that is the hallmark of disseminating tumor cells. CSCs are enriched near macrophages, particularly near macrophage-containing intravasation sites called Tumor Microenvironment of Metastasis (TMEM) doorways. Substantial enrichment of CSCs occurs on association with TMEM doorways, contributing to the finding that CSCs represent >60% of circulating tumor cells. Mechanistically, stemness is induced in non-stem cancer cells upon their direct contact with macrophages via Notch-Jagged signaling. In breast cancers from patients, the density of TMEM doorways correlates with the proportion of cancer cells expressing stem cell markers, indicating that in human breast cancer TMEM doorways are not only cancer cell intravasation portals but also CSC programming sites.

Mucoepidermoid carcinoma (MEC) is a relatively common salivary tumor with varying potential for aggressive behavior. Mucoepidermoid carcinoma grading has evolved from descriptive two-tiered schemata to more objective three-tiered systems. In 2001, we published a grading system Brandwein et al. in Am J Surg Pathol 25:835-845, (2001) which modified the prevailing criteria of Auclair et al. in Cancer 69:2021-2030 (1992), and included additional features of aggressive MEC. Here we seek to validate our modified grading system in a new multicenter cohort. The retrospective cohort consisted of 76 patients with confirmed MEC and known outcome data. The resection specimens were reviewed and uniformly graded according to our modified criteria Brandwein et al. in Am J Surg Pathol 25:835-845 (2001), and the Auclair criteria Auclair et al. in Cancer 69:2021-2030, (1992), Goode et al. in Cancer 82:1217-1224, (1998). Case distribution was as follows: Montefiore Medical Center: 41 (1977-2009), University of Alabama at Birmingham: 21 (1999-2010), and Rhode Island Hospital: 14, (1995-2011). Patient age ranged from 7 to 81 years (mean 51 years). The female to male ratio was 3:1. The most commonly involved sites were: parotid: n = 39 (51%), palate: n = 10 (13%), retromolar trigone: n = 6 (8%), buccal: n = 5 (7%), and submandibular gland: n = 5 (7%). The modified criteria upgraded 41% MEC; 20/25 MEC from AFIP Grade 1 to Grade 2 and 5/25 from AFIP grade 1 to grade 3. Eleven patients had positive lymph nodes; the AFIP MEC grade for cases were: grade 1-3/11, Grade 2-1/11, and grade 3-7/11; the modified grading criteria distribution for these cases were Grade 1: 0/11, grade 2: 1/11, and grade 3: 10/11. Nine patients developed disease progression after definitive treatment. High-stage and positive lymph node status were significantly associated with disease progression (p = 0.0003 and p < 0.0001, respectively). For the nine patients with disease progression, the modified grading schema classified eight MEC as grade 3 and one as grade 2. By comparison, the AFIP grading schema classified three of these MEC as grade 1, and the remaining six as grade 3. Despite the fact that this multicenter retrospective study accrued 76 patients with outcome, the predictive performance of the two grading schema could not be compared due to the few patients who experienced disease progression and were also reclassified with respect to grade (n = 3).