Abstract P5-01-04: In vivo lymphatic imaging of a human inflammatory breast cancer model

Background: Inflammatory breast cancer (IBC) is the most aggressive but poorly understood type of breast cancer. IBC constitutes only appoximately 5% of all newly diagnosed breast cancers, yet responsible for 8-10% of breast cancer-related deaths. Unfortunately, there are no definitive molecular or pathological, early diagnostic criteria for IBC. IBC grows in nests or sheets, spreading outward into the skin and eventually distant sites through dermal lymphatic vessels; therefore, one of the key pathological characteristics of IBC is dermal lymphatic invasion by tumor emboli, which can lead to obstruction of the lymphatic drainage possibly causing the clinical inflammatory features of diffuse erythema, rapid breast enlargement and edema as indicated by peau d’orange (orange peel) appearance covering at least a third of the breast surface. However, relatively little is known about the role of lymphatic function in IBC growth and metastasis. The purpose of this study was to non-invasively and longitudinally image changes of lymphatic drainage patterns in mice bearing the triple negative, human IBC SUM149 cells, which were stably transfected with iRFP gene reporter (iRFP-SUM149) in order to better monitor tumor growth and metastasis. Methods: Eight to ten weeks old female non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice were housed and fed special sterilized pelleted food and sterilized water. Two weeks after feeding special diets, mice were subcutaneously injected with iRFP-SUM149 cells in the left hindlimb or orthotopically in the left inguinal mammary fat pad (MFP). Fluorescence images were acquired immediately after and for up to 10 mins after i.d. injection of indocyanine green (ICG) using a custom-built NIRF imaging system. To achieve a greater magnification, a macrolens was used. Results: Our NIRF imaging data showed gradual changes of lymphatic vessels around the tumor. In mice with an orthotopic tumor, ICG accumulation was observed in the distal peritumoral region at up to 3 weeks p.i., indicative of the start of tumor obstruction of normal lymphatic drainage. As tumors grew, the greater extent of lymph flow, but not all, was obstructed by a tumor, resulting in dermal backflow and thus staining more lymphatic capillaries and eventually rerouting of lymphatic drainage was detected due to complete obstruction of lymph flow by a tumor. Similar to an orthotopic model, mice with a s.c. tumor also showed altered lymphatic drainage patterns during tumor growth. Interestingly, extravasation of ICG into iRFP-SUM149 was detected at 3 weeks p.i., due to leaky lymphatic vessels. A similar lymphatic phenotype has also been observed in IBC patients. Previously, we have imaged atypical tortuous lymphatics and altered lymphatic drainage in the arm and affected breast of a patient with IBC using clinical NIRF imaging developed in our team to image as deep as 3-5 cm with a microdose of ICG. Conclusions: Longitudinal, non-invasive imaging of lymphatic functional and architectural changes provides a new method to dynamically monitor lymphatic response to IBC growth and metastasis. Citation Format: Sunkuk Kwon, Germaine Agollah, Grace Wu, Eva M Sevick-Muraca. In vivo lymphatic imaging of a human inflammatory breast cancer model [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-01-04.