Expression of Lymphangiogenic Factors and Evidence of Intratumoral Lymphangiogenesis in Pancreatic Endocrine Tumors

Abstract

Lymphangiogenesis is thought to promote the progression of malignant tumors. Because the lymphangiogenic factors vascular endothelial factor (VEGF)-C and -D are expressed in endocrine cells, we investigated their expression in pancreatic endocrine tumors (PETs) and correlated these data and intratumoral lymph vessel density (iLVD) with clinicopathological features. Lymph vessels were identified with anti-podoplanin antiserum and with podoplanin/proliferating cell nuclear antigen double labeling. PETs (n ‫؍‬ 104) were investigated by immunohistochemical staining for VEGF, basic fibroblast growth factor, and VEGF-C expression. VEGF-C and VEGF-D mRNA were quantified by real-time reverse transcriptase-polymerase chain reaction. PETs showed higher iLVD than normal pancreata, but iLVD did not discriminate between benign and malignant PETs. In PETs proliferating lymph vessels were identified. High iLVD was associated with lymph vessel invasion and it was more frequent in angioinvasive/metastatic tumors than in grossly invasive tumors. The biological behavior of pancreatic endocrine tumors (PET) is difficult to predict on the basis of histological criteria. In the absence of clear signs of malignancy, such as invasion of adjacent organs, angioinvasion, or metastasis, the prognosis remains uncertain. Because most human carcinomas metastasize via lymphatic invasion, lymph node metastasis is a key prognostic factor for the clinical outcome. By which mechanism tumor cells spread through the lymph vessels is unknown. One proposed mechanism is the induction of new lymph vessels by tumor or inflammatory cells, facilitating lymphangioinvasion. Intratumoral lymph vessels have been detected in head and neck squamous cell carcinomas 1,2 and in cutaneous melanomas. 3,4 In squamous cell carcinomas intratumoral lymph vessel density (iLVD) has been shown to correlate with lymph node metastasis, whereas the results for melanomas are inconsistent. Beasley and colleagues 1 and Straume and colleagues 3 showed that intratumoral lymphatic endothelial cells were capable of proliferation, suggesting de novo lymphangiogenesis. No evidence of intratumoral lymph vessels was found in ovarian, 5 liver, 6 breast, 7,8 or cervical carcinomas. 9

Lymphatic microvessel density as prognostic marker in colorectal cancer

“…We found that intratumoral lymphatic vessels are present in colon cancer, using D2-40. Similar to previous studies, we found that most of intratumoral lymphatics are small and flattened, 23,32,34 contrasting the widely open lymphatics in peritumoral regions.…”

“…23,24 However, Clarijs et al, 25 reported newly formed lymph vessels within the solid tumors using double staining with CD31 and PAL-E. Others have recently observed intratumoral lymphatics in melanomas, 26,27 breast, 28 head and neck, 29,30 pancreatic carcinoma, 31 and islet cell tumor. 32 A recent study detected intratumoral lymphatics in 91% of colorectal carcinoma. 33 Our results are in agreement with the later study.…”

Lymphatic and angiogenic characteristics in breast cancer: morphometric analysis and prognostic implications

“…The present study examined 85 specimens and proliferative lymphatics were detected in 25 (29%) with PF-L ranging from 0 to 2.2%. PF-L ranged from 0 to 3% in studies of other tumour types, [36,42,43]. The low PF-L is undoubtedly due to the inability of the methodology to accurately detect all dividing LECs within tumours, and is most probably underestimated as sprouting of new vessels begins at different levels along the lymphatic vessel [44].…”

The extent of retraction clefts correlates with lymphatic vessel density and VEGF-C expression and predicts nodal metastasis and poor prognosis in early-stage breast carcinoma

“…2 In recent years, several markers specific for lymphatic endothelium, including vascular endothelial growth factor receptor-3 (VEGFR-3), the transmembrane proteins LYVE-1 and podoplanin, and the transcription factor Prox-1, have been used to evaluate intratumor lymphatic vessels in solid tumors, including breast cancer. [4][5][6] Intratumor lymphatic endothelial cells were shown to be capable of proliferation in some types of cancer, suggesting de novo lymphangiogenesis. 4,7 These studies also showed a correlation between lymphatic vessel density and nodal metastasis in some tumors, 8 but not in others.…”