Estrogen may induce breast cancer

Preface

We chose this topic cause for us it is very interesting and an up to date topic. In this paper we wanted to get a better knowledge about estrogen, what preparations that contain higher level and what risks it may has on a human body. We have used textbooks and mostly medical articles posted on pubmed.com to get more information.

Introduction

Breast cancer is the most common type of cancer among women in the Western world, and breast cancer incidences have increased by 2-3 % annually during the past 50 years. Several factors are playing a role in how women around the world get breast cancer, both lifestyle and genetics inherited play a crucial role. Several studies have been done proving that prolonged intake of the hormone estrogen over several years may increase the possibility to develop breast cancer. Estrogen intake in form of birth control pills and HRT (hormone replacement therapy) linked to menopause is the most common used preparations.

Physiology background

Estrogens are hormones which occur naturally and synthetically and are principally associated with ovarian cycle, pregnancy and parturition together with progesterone and gonadotropins. The most important hormones are those belonging to the group of steroids and are produced by the granulosa cells of follicles in the ovary, placenta and adrenal cortex in women. Estrogens comprises of estradiol-17β, estrone and estriol where estradiol is the most predominant in both pregnant and non-pregnant. Estrogen regulates the proliferation of normal and neoplastic breast epithelium. It triggers its effect on women genital development and the organism as a whole and is also to be found in bone structure. Some of its tasks relevant to this topic are to stimulate follicular development, development of secondary sexual characteristics like breasts by stimulating duct growth, secretory activity of uterine ducts and more. Progesterone works close with the estrogens and it is a part of estrogens synthesis. It is a steroid sex hormone produced by corpus luteum of the ovary, placenta and adrenal cortex. Main task is to ensure secretory changes in the uterus in the other half of the menstrual cycle. In this way the uterus is ready to receive a fertilized egg. Progesterone also acts relaxing on the musculature of the uterus that will prevent repelling of the fertilized egg. Also promotes endometrial gland growth. Both progesterone and estrogens are steroid hormones which are synthesized from the cholesterol in the blood. The pathway starts with the: cholesterol → pregnenolone → progesterone → testosterone → estrogens, (from the textbook “Functional anatomy and physiology of domestic animals, 4th edition”). The estrous cycle starts after puberty and is the period between two subsequent ovulations. It consists of four phases: proestrus, estrus, metestrus and diestrus. The length of estrus cycle in humans is 28 days and in mammals usually 21 days, but it differs from species to species. The estrous cycle is interrupted by pregnancy. Estrogen level is highest near the end of the follicular phase right before ovulation (menstrual cycle). Estrogens have two receptors named ERα and ERβ and they are very alike in the amino acid level in both the DNA binding domain and the ligand binding domain. They are represented in many tissues, in some organs they are equally and in others one of them predominates. At the same time they may be represented in the same tissue, but in different cell types. The ERα is mainly represented in the uterus, ovary (theca cells), bone, breast, liver, white adipose tissue and more. While the ERβ is mainly represented in colon, ovary (granulosa cells), bone marrow, salivary gland, vascular endothelium and more.