Presence Of Cancer-Associated Fibroblasts Inversely Correlates With Schwannian Stroma In Neuroblastoma Tumors

Stromal cells play a central role in the regulation of tumor angiogenesis. Recent studies have shown that stromal myofibroblasts [cancer-associated fibroblasts] actively promote tumor growth and enhance tumor angiogenesis in many types of adult carcinomas. To evaluate the role cancer-associated fibroblasts play in neuroblastoma angiogenesis and investigate their relationship to stromal Schwann cells, we quantified cancer-associated fibroblasts in 60 primary neuroblastoma tumors and in a novel neuroblastoma xenograft model in which murine Schwann cells were induced to infiltrate into the tumor stroma. Tumor sections were examined for presence of microvascular proliferation, a hallmark of tumor angiogenesis. Cancer-associated fibroblasts were characterized by positive immunostaining for α-smooth muscle actin (α-SMA) and were distinguished from pericytes by staining negatively for high-molecular weight caldesmon. α-SMA positive cells were quantified and their number was defined as high when >1.0% of the area was positive. Associations between high cancer-associated fibroblast number, microvascular proliferation, and established prognosticators were analyzed. High numbers of cancer-associated fibroblasts were associated with Schwannian Stroma-poor histopathology and microvascular proliferation. Thirty-seven (80%) of the 46 Schwannian Stroma-poor tumors had high numbers of cancer-associated fibroblasts in the tumor stroma compared to only 2 (14%) of the 14 Schwannian Stroma-rich/dominant tumors (p<0.001). Thirty-three (89%) of 37 tumors with microvascular proliferation had high numbers of cancer-associated fibroblasts compared to 9 (40%) of 22 tumors without microvascular proliferation (p <0.001). In the xenografts with infiltrating Schwann cells (n=10), the number of cancer-associated fibroblasts/mm(2) was ~7-fold less than in the control xenografts without stromal Schwann cells (n=9) (mean of 51 ± 30 vs 368 ± 105, respectively; p<0.001). Thus, cancer-associated fibroblasts were inversely associated with presence of Schwann cells, suggesting that Schwann cells may prevent the activation of fibroblasts. A deeper understanding of the role cancer-associated fibroblasts play in neuroblastoma angiogenesis may guide future development of stroma-directed therapeutic strategies.