Hormone Therapy for Uterine Cancer: Progestins and Other Options

Hormone therapy works by slowing the growth of certain uterine cancer cells by blocking or changing the levels of specific hormones. The two key hormones involved in uterine cancer are estrogen and progesterone. Hormone therapy for uterine cancer may be prescribed for those facing advanced or recurrent uterine cancer, or those who do not want to or are unable to undergo a hysterectomy. They can help preserve fertility if needed and can also be used as an adjuvant therapy to help control the spread of cancer cells left behind after surgery or radiotherapy. However, if your cancer is not hormone receptor positive, you may not be eligible for this therapy.

The most commonly used form of hormone therapy for uterine cancer is progestins. These are man-made versions of progesterone that are produced in a lab. They work by helping to limit the growth of uterine cancer cells by counteracting the effects of estrogen. Some options include medroxyprogesterone acetate (Provera) and megestrol acetate (Megace). These are oral medications.

The most common progestin side effects include:

• Breast tenderness
• Menstrual changes, minor vaginal bleeding or vaginal secretions
• Headaches
• Nausea
• Dizziness
• Insomnia, sleepiness or fatigue
• Bloating or fluid retention

If you have not undergone a hysterectomy, another option is a levonorgesterel IUD, a progestin-releasing device placed in your uterus. This is a small, plastic T-shaped device that releases the progestin levonorgestrel, which will be put in place by a healthcare provider. As the IUD only releases the drug into your uterus, only small amounts of the hormone will enter your bloodstream.

After the device has been placed in your uterus, you may feel two threads in the vagina. However, these threads will not extend outside of your body.

The most common levonorgesterel side effects include:

• Abdominal cramping, bleeding or dizziness during and after placement
• Menstrual changes or vaginal discharge
• Cysts on the ovary (these will usually disappear after a few months but may sometimes require surgery)
• Abdominal pain or cramping
• Infection of the outer part of the vagina
• Headaches or migraines

Aromatase inhibitors may be used to block the production of estrogen by the body. Options include anastrozole (Arimidex), letrozole (Femara) or exemestane (Aromasin). These drugs are usually taken orally. Common side effects include hot flashes, fatigue, muscle and joint stiffness.

Fulvestrant (Faslodex) is another anti-estrogen drug, known as a selective estrogen receptor degrader. By breaking down estrogen receptors, it prevents estrogen from binding to cancer cells, blocking them from directing further cancer growth. Fulvestrant is delivered by injections. Common side effects include hot flashes, night sweats, headaches, nausea, fatigue and loss of appetite.

Cyclin-dependent kinase (CDK) 4/6 inhibitors prevent cancer cells from multiplying. One example is ribociclib (Kisqali). Common side effects include fatigue and increased risk of infection due to low white blood cell count.