: a new concept of the tumor-microenvironment interface as a dynamic tissue zone vital for tumor progression.
Criteria traditionally used to define tumor margins may not clearly distinguish between tumor and normal tissues, and can thus result in tumor cells remaining at the surgical site—a frequent cause of tumor recurrence. Efforts to define tumor margins using molecular criteria have achieved limited success because they typically fail to consider the tumor microenvironment (TME). Here, we took both tumor cells and the TME into account in delineating tumor margins, classifying breast cancer tissue into a tumor zone (TZ), a normal zone (NZ), and the novel concept of interface zone (IZ). Collectively, these results suggest that the IZ represents a dynamic zone vital for tumor progression whose boundary can be applied as a reliable molecular tumor-margin marker.
Interface zone represents a dynamic zone vital to tumor progression and is the site of epithelial-mesenchymal transition, an interpretation supported by cadherin switching and overexpression of laminin-332 and MMP14. As such, the IZ represents a reliable molecular tumor-margin marker in breast cancer.
Increased binding of laminin-332 to integrin α6β4 delivers a tumor progression signal through PI3K and RAC1. This signaling depends on the overexpression of laminin-332 and integrin α6β4. TWIST, an upstream modulator of SNAIL, is mainly expressed in the TZ and is present at the lowest levels in the IZ. SNAIL and ZEB1 are upregulated in the IZ in conjunction with downregulation of miR200c. MMP2, which is the MMP primarily responsible for processing laminin-332 and enzymatically degrading structural molecules in the TME, is activated by MMP14 and MMP15. E-cadherin downregulation by EMT inducers together with enzymatic degradation of E-cadherin by MMPs contributes to cadherin switching, which manifests most notably as a loss of E-cadherin. MMP11, which is expressed in tumor and stromal cells undergoing EMT, begins to be expressed in the TZ and is largely maintained in the IZ.
*Model depicting events occurring in the interface zone during tumor progression.
A. Quantitative comparison of LAMA3, LAMC2, ITGA6, and ITGB4 transcripts using real-time PCR showing upregulation of LAMA3, LAMC2, ITGA6, and ITGB4 in the IZ compared with the TZ and NZ.
B. Expression of laminin-332 and integrin α6β4 in each tissue zone, and relative intensity of laminin-332 and integrin α6β4 signals.
C. Comparison of laminin-332 binding to integrin α6β4 determined using coimmunoprecipitation with antibodies against laminin-332 and integrin β4.
D. Immunohistochemical analysis of laminin-332 expression in the IZ using an anti-laminin γ2 antibody.