Sex differences in the incidence of colorectal cancer: an exploration of oestrogen and progesterone receptors.

Sex differences exist in the site specific incidences of colorectal cancer. The increased incidence of colonic cancer in women with breast cancer and the protective effect of increasing parity suggest a role for sex hormones. To explore the molecular basis, the expression of messenger RNA for oestrogen and progesterone receptors in the large bowel has been studied. With northern and dot blot analyses mRNA coding for oestrogen receptor and progesterone receptor in large bowel cancers and corresponding normal mucosa and in adenomatous polyps has been identified. There were no significant differences in receptor mRNA concentrations between males and females or between cancers, normal mucosae, and polyps, except for rectal cancers, which had higher progesterone receptor concentrations than corresponding normal tissue. Oestrogen and progesterone receptor mRNA concentrations were strongly correlated in both cancers and normal tissues. Enzyme immunoassay for oestrogen receptor gave values of 1.2-7.4 fmol/mg total protein, an amount similar to that seen in normal breast tissue. Oestrogen receptor protein and mRNA for oestrogen receptor and progesterone receptor are present in the large bowel.