A Novel Preclinical Murine Model to Monitor Inflammatory Breast Cancer Tumor Growth and Lymphovascular Invasion

SIMPLE SUMMARY: Lymphovascular invasion (LVI), the presence of tumor cells in lymphovascular spaces, is associated with an increased risk of metastasis and is considered an independent prognostic indicator. LVI is a clinicopathological hallmark of inflammatory breast cancer (IBC), an understudied but highly lethal variant presenting as diffuse tumor cell clusters (tumor emboli) invading throughout the breast and dermal lymphatics, causing breast erythema and edema and often without a distinct tumor mass. There is a lack of preclinical IBC models that monitor spatial and temporal changes during growth and migration of individual tumor clusters. Herein, we generated a transgenic murine model with red fluorescent lymphatics that, with implantation of tumor cells in a dorsal skin window chamber, simulate IBC characteristics. This model enables intravital imaging and quantitative analysis of collectively migrating tumor cells and vessel density in the local tumor microenvironment, an innovation that can be widely applied to various cancers exhibiting LVI. ABSTRACT: Inflammatory breast cancer (IBC), an understudied and lethal breast cancer, is often misdiagnosed due to its unique presentation of diffuse tumor cell clusters in the skin and dermal lymphatics. Here, we describe a window chamber technique in combination with a novel transgenic mouse model that has red fluorescent lymphatics (ProxTom RFP Nu/Nu) to simulate IBC clinicopathological hallmarks. Various breast cancer cells stably transfected to express green or red fluorescent reporters were transplanted into mice bearing dorsal skinfold window chambers. Intravital fluorescence microscopy and the in vivo imaging system (IVIS) were used to serially quantify local tumor growth, motility, length density of lymph and blood vessels, and degree of tumor cell lymphatic invasion over 0–140 h. This short-term, longitudinal imaging time frame in studying transient or dynamic events of diffuse and collectively migrating tumor cells in the local environment and quantitative analysis of the tumor area, motility, and vessel characteristics can be expanded to investigate other cancer cell types exhibiting lymphovascular invasion, a key step in metastatic dissemination. It was found that these models were able to effectively track tumor cluster migration and dissemination, which is a hallmark of IBC clinically, and was recapitulated in these mouse models.