High levels of dietary soy decrease mammary tumor latency and increase incidence in MTB-IGFIR transgenic mice.

Area of Science:

• Oncology
• Nutritional Science
• Molecular Biology

Background:

• Epidemiological studies suggest Asian diets, rich in soy protein, are associated with reduced breast cancer risk in women.
• Disentangling soy's benefits from other lifestyle and environmental factors in human studies is challenging.
• Rodent models offer a viable alternative for studying the long-term effects of dietary soy.

Purpose of the Study:

• To investigate the impact of soy-based diets on mammary tumor development in a transgenic mouse model.
• To determine if soy protein influences tumor incidence, latency, and metastatic potential.
• To explore the role of estrogen receptor signaling in soy-induced mammary tumorigenesis.

Main Methods:

• Utilized MTB-IGFIR transgenic mice overexpressing the type I insulin-like growth factor receptor (IGF-IR).
• Administered soy-based or casein-based diets throughout development.
• Initiated mammary tumors at different developmental stages by controlling IGF-IR transgene expression.

Main Results:

• Mice fed soy diets exhibited increased mammary tumor incidence and earlier tumor onset compared to casein-fed mice.
• Elevated expression of estrogen receptor signaling markers (Pgr, Areg) was observed in mammary tissue of soy-fed mice.
• Soy-fed mice showed increased expression of metaplastic markers (cytokeratins 5/14, p63) but reduced lung metastases.

Conclusions:

• Very high levels of dietary soy protein appear to promote mammary tumor development and reduce latency, potentially via estrogen receptor activation.
• Further research is needed to ascertain if moderate soy consumption can inhibit oncogene-induced mammary tumorigenesis.