Low-thiamine diet increases mammary tumor latency in FVB/N-Tg(MMTVneu) mice.

We have previously described the down-regulation of thiamine transporter gene expression in breast cancer, and others have shown an epidemiologic relationship between obesity and breast cancer. To further explore the relationship of thiamine, fat, and breast cancer, we exposed FVB/N-Tg(MMTVneu)202Mul/J female mice to four diets that varied in fat and thiamine content (15 mice per group). The high-fat (HF) diet contained 60 % of calories from fat and the normal-fat (NF) diet contained 10 % of calories from fat. The normal-thiamine (NT) diet contained 6 mg thiamine per 4057 kcal and the low-thiamine (LT) diet contained 2 mg thiamine/4057 kcal. Tumor latency was 203 days from date of birth for the HF/NT group, 210 days for the HF/LT group, 225 days for the NF/NT group, and 295 days for the NF/LT group (p = 0.01). The time to endpoint of a mammary tumor volume > 1000 mm3 was 231 days for the HF/NT group, 238 days for the HF/LT group, 257 days for the NF/NT group, and undefined (>310 days) for the NF/LT group (p < 0.001). The high-fat groups were heavier than the normal-fat groups, and the low-thiamine group had a lower serum thiamine level than the normal-thiamine group. There were no differences in the number of pulmonary metastases between groups. This study demonstrates a potential role for dietary thiamine, and an interaction between thiamine and fat, in breast cancer progression.