Dietary lignin, an insoluble fiber, enhanced uterine cancer but did not influence mammary cancer induced byN‐methyl‐N‐nitrosourea in rats

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Abstract
Previous investigations suggested potential breast cancer‐preventive properties of dietary fiber from cabbage. The purpose of the present investigation was to determine whether lignin, a component of cabbage fiber, would protect against mammary carcinogenesis by N‐methyl‐N‐nitrosourea (MNU) in Sprague‐Dawley rats. A six‐week study was conducted using diets containing 0.5–5% dietary wood lignin (a readily, available, purified source). These diets were well tolerated by the rats, and a carcinogenesis study using 5 mg MNU/100 g body wt iv at 50 days of age was conducted, with the 2.5% lignin diet fed from 6 through 8 weeks of age followed by 5% lignin diet until 20 weeks after MNU. Dietary lignin and MNU treatment increased food consumption (p < 0.05), and body weight was slightly reduced at 10 and 20 weeks after MNU in the MNU‐5% lignin diet group (p < 0.05). Serum estradiol was not altered by dietary lignin or MNU treatment, but uterine weights were highest in the MNU‐control diet group 4 and 12 weeks after MNU. Expression of creatine kinase B, an estrogen‐responsive gene, was lower in the uteri of the MNU‐lignin diet group than in other groups at 20 weeks. Mammary carcinogenesis was not altered by dietary lignin. However, uterine endometrial adenocarcinoma was observed only in the MNU‐lignin diet group (4 carcinomas/40 effective rats) (p < 0.05).