Dietary Phytoestrogen Increases Tumour Size and the Frequency of Circulating Tregs in a B16-F10 Murine Melanoma Tumour Model

Background: Clinical studies show strong associations between hormone levels, particularly estrogens and the development of skin cancers. Cutaneous melanoma is considered a hormone-related tumour; however, their role in melanoma progression remains unclear. Objective: To investigate the effects of a phytoestrogen-rich diet on melanoma tumour initiation and development using a syngeneic mouse model. Patients and Methods: Mice were fed either a phytoestrogen-rich or low control diet and injected subcutaneously with 5 × 10⁵ syngeneic melanoma cells (B16-F10). After 10–12 weeks, tumours and spleens were collected. Tumour size and weight were measured, and quantitative PCR (qPCR) was performed to analyse the expression of estrogen receptor (ER) α and β. Regulatory T cells (Tregs) from splenocytes was assessed via flow cytometry. Results: Mice consuming the phytoestrogen-rich diet exhibited significantly larger tumours compared to those on the control diet. Phytoestrogens in the diet up regulated ERβ and down regulated ERα mRNA expression in tumour tissue. A significant increase in the proportion of splenic Tregs was observed in tumour-bearing mice fed a phytoestrogen-rich diet. Conclusion: This study highlights the influence of dietary composition on tumour growth and associated immune responsiveness, emphasising the need to account for dietary factors in experimental designs and their potential impact on tumour biology. Keywords: Phytoestrogen, T-regulatory cells, Murine melanoma tumours, Flow cytometry.