Uterine fibroids, are also called leiomyomas. Leio- means smooth, myo- means muscle, and -oma means tumor, so these are benign smooth muscle tumors of the uterus.
In fact, fibroids are the most common type of tumor in females.
The uterus is a hollow organ that sits behind the urinary bladder and in front of the rectum.
The top of the uterus above the openings of the fallopian tubes is called the fundus, and the region below the openings is called the uterine body.
The uterus tapers down into the uterine isthmus and finally the cervix, which protrudes into the vagina.
Zooming into the cervix, there are two openings, a superior opening up top, and an inferior opening down below, both of which have mucus plugs to keep the uterus closed off except during menstruation and right before ovulation.
The uterus is anchored to the sacrum by utero- sacral ligaments, to the anterior body wall by round ligaments, and it’s supported laterally by cardinal ligaments as well as the mesometrium, which is part of the broad ligament.
The wall of the uterus has three layers: the perimetrium, which is a layer continuous with the lining of the peritoneal cavity, the myometrium, which is made of smooth muscle that contracts during childbirth to help push the baby out, and the endometrium, a mucosal layer, that undergoes monthly cyclic changes.
Now, uterine fibroids are smooth muscle tumors, and they’re monoclonal meaning that they arise from a single cell of the myometrium that starts dividing uncontrollably.
Overall, fibroids most commonly affect women of African descent.
They’re sometimes linked to a genetic mutation, with the most common being a somatic mutation with the mediator complex subunit 12 or MED12 gene.
Mediator complex subunit 12 is part of a group of proteins that control gene activity by regulating how transcription factors bind to RNA polymerase II.
Another factor in fibroid development is steroid hormones.
Fibroids have a love affair with estrogen and progesterone!
Fibroids upregulate their receptors for these two hormones and also produce a lot of aromatase, an enzyme that converts androgens into estrogen.
When these hormones bind to the myometrium cells, it has a mitogenic effect, meaning it promotes mitosis.
Estrogen specifically upregulates growth factors, like IGF- 1, EGFR, and TGF- beta1, and progesterone upregulates EGF, TGF- beta1, and TGF- beta3.
So, the more estrogen and progesterone available, the more a fibroid is likely to grow.
This is why fibroids typically affect pre- menopausal females and why they grow rapidly during pregnancy - when there’s a lot of estrogen around.
Another risk factor for developing a fibroid is never having a pregnancy and breastfeeding, and having many menstrual cycles - each with a wave of hormones.
Finally, a historical risk factor that is less relevant now, was exposure to diethylstilbestrol, an estrogen medication that used to be given to pregnant women.
Finally, in rare cases, fibroids are linked to a hereditary condition called hereditary leiomyomatosis and renal cell carcinoma syndrome, also called Reed’s syndrome, which causes skin and uterine fibroids and an aggressive form of papillary renal cell cancer.
Fibroids can be described based on where they are located in the uterus.