In a previous study, our group has shown that the expression of caveolin-1 (CAV1) in normal tissue surrounding a primary breast cancer is a powerful prognostic indicator of subsequent metastatic disease. Whilst reports linking expression of CAV1 within breast tumour cells to clinical outcome have not led to any clear conclusions, our finding of a strong positive correlation between loss of CAV1 expression in breast tumour stroma and poor prognosis (p<0.0001)1, is novel and exciting as it offers the potential of a reliable prognostic indicator of metastatic disease.
Tumours arising from non- or weakly metastatic mammary cells grow at a faster or similar rate when co-injected with CAV1 null mammary fibroblasts. In contrast, co-injection with CAV1 expressing mammary fibroblasts has a suppressive effect on tumour growth. Metastasis to lung was significantly higher in mice with resected primary tumours that arose from the co-inoculation of weakly metastatic mammary cells and CAV1 null mammary fibroblasts (p = 0.0241), in addition to a significant increase in individual lung tumour nodule size.
To further understand the consequences of the loss of stromal CAV1, profiling of CAV1 expressing and null mouse mammary fibroblasts was conducted using cytokine arrays and cDNA microarrays. Differences in the secretion of known CAV1 associated cytokines such as RANTES, Gas6 and IL-6 were observed, with no significant changes in their expression.
Results from this study demonstrate that stromal CAV1 is an important prognostic factor, and may even be contributing directly to breast cancer progression. Based on these findings, a stromal targeted therapy to that restores or substitutes for CAV1 activity in stromal cells, or that targets CAV1 regulated cytokines such as Gas6, may be a viable therapy in the treatment of breast cancer metastasis.