No abstract

The lymphatic system transports interstitial fluid and macromolecules from tissues back to the blood circulation, and plays an important role in the immune response by directing the traffic of lymphocytes and antigen-presenting cells. The lymphatic system also constitutes one of the most important pathways of tumor dissemination. In many human cancers, increased expression of vascular endothelial growth factor-C (VEGF-C) is correlated with regional lymph node metastases. Experimental studies using transgenic mice overexpressing VEGF-C or xenotransplantation of VEGF-C-expressing tumor cells into immunodeficient mice have demonstrated a role for VEGF-C in tumor lymphangiogenesis and the subsequent formation of lymph node metastases. However, there is at present little evidence for lymphangiogenesis in human tumors and the relative importance of preexisting vs. newly formed lymphatics for metastasis in humans remains to be determined. Nonetheless, the striking correlation between the levels of VEGF-C in primary human tumors and lymph node metastases predicts its importance in cancer spread. Aside from promoting lymphangiogenesis, VEGF-C may also activate lymphatics to promote tumor cell chemotaxis, lymphatic intravasation and hence tumor cell dissemination.

Background-Long-term patency of conventional synthetic grafts is unsatisfactory below a 6-mm internal diameter.Poly(⑀-caprolactone) (PCL) is a promising biodegradable polymer with a longer degradation time. We aimed to evaluate in vivo healing and degradation characteristics of small-diameter vascular grafts made of PCL nanofibers compared with expanded polytetrafluoroethylene (ePTFE) grafts. Methods and Results-We prepared 2-mm-internal diameter grafts by electrospinning using PCL (M n ϭ80 000 g/mol).Either PCL (nϭ15) or ePTFE (nϭ15) grafts were implanted into 30 rats. Rats were followed up for 24 weeks. At the conclusion of the follow-up period, patency and structural integrity were evaluated by digital subtraction angiography. The abdominal aorta, including the graft, was harvested and investigated under light microscopy. Endothelial coverage, neointima formation, and transmural cellular ingrowth were measured by computed histomorphometry. All animals survived until the end of follow-up, and all grafts were patent in both groups. Digital subtraction angiography revealed no stenosis in the PCL group but stenotic lesions in 1 graft at 18 weeks (40%) and in another graft at 24 weeks (50%) in the ePTFE group. None of the grafts showed aneurysmal dilatation. Endothelial coverage was significantly better in the PCL group. Neointimal formation was comparable between the 2 groups. Macrophage and fibroblast ingrowth with extracellular matrix formation and neoangiogenesis were better in the PCL group. After 12 weeks, foci of chondroid metaplasia located in the neointima of PCL grafts were observed in all samples. Conclusions-Small-diameter PCL grafts represent a promising alternative for the future because of their better healing characteristics compared with ePTFE grafts. Faster endothelialization and extracellular matrix formation, accompanied by degradation of graft fibers, seem to be the major advantages. Further evaluation of degradation and graft healing characteristics may potentially lead to the clinical use of such grafts for revascularization procedures.

The lymphatic system is the primary pathway of metastasis for most human cancers. Recent research efforts in studying lymphangiogenesis have suggested the existence of a relationship between lymphatic vessel density and patient survival. However, current methodology of lymphangiogenesis quantification is still characterised by high intra-and interobserver variability. For the amount of lymphatic vessels in a tumour to be a clinically useful parameter, a reliable quantification technique needs to be developed. With this consensus report, we therefore would like to initiate discussion on the standardisation of the immunohistochemical method for lymphangiogenesis assessment. Metastasis is the leading cause of cancer mortality. Metastatic cancer cells can escape from their site of origin and spread to distant organs through invasion of the vascular system and/or the lymphatic system. Tumour vascularisation is widely accepted as a bona fide indicator of tumour growth, metastases and patient survival. In 1996, Peter Vermeulen et al (1996) published a first international consensus on the methodology and criteria of the evaluation of angiogenesis quantification in solid tumours and 5 years later, a second consensus report, in which new concepts and mechanisms of tumour vascularisation were integrated, appeared (Vermeulen et al, 2002). Both reports were aimed at improving the standardisation of angiogenesis quantification in order to allow intratumourous microvessel density to be applied as a prognostic indicator and, moreover, as a reliable predictor of the risk of malignant transformation of premalignant lesions and of response to cancer treatment. Contrary to angiogenesis, the de novo formation of lymphatic vessels or lymphangiogenesis and its role in promoting the metastatic spread of tumour cells has only recently become a focal point of cancer research with an increasing number of studies showing a relationship between patient survival and lymphatic density in different tumour types. In order to confirm the potential prognostic value of lymphangiogenesis in patients with cancer, a quantification method that is characterised by a low intra-and interobserver variability needs to be developed. In this first consensus report, we would like to provide an overview of current concepts of the lymphatic vasculature and its regulating factors and propose guidelines for the estimation of the ongoing lymphangiogenesis in solid human tumour sections.