Dr Sithembile Ngidi describes the different types of hormone therapy used to treat prostate cancer.
To understand the who, what, where, why and how of hormone therapy, it’s important to start at the basics. That would be understanding the driving hormone behind prostate cancer and its treatment: testosterone.
This is the primary male hormone that’s key in the growth and function of sex organs, like the testes, prostate and other tissues.
Testosterone is an androgen (a natural steroid hormone) and promotes growth in tissues with androgen receptors. It exerts two types of effects on the body:
- Anabolic effects – growth of muscle mass and strength; increased bone density; stimulation of linear growth (height), etc.
- Androgenic effects – maturation of sex organs; deepening of voice; and growth of hair.
Testosterone is produced mainly in the Leydig cells in testes. The number and production of these Leydig cells is regulated by two hormones: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The amount of testosterone produced in the Leydig cells is also controlled by LH.
Though, the amount of testosterone synthesised is regulated by the hypothalamic–pituitary–testicular axis (the hypothalamus and pituitary are organs in the brain).
When testosterone levels are low, gonadotropin-releasing hormone (GnRH) is released by the hypothalamus, which stimulates the pituitary gland to release FSH and LH. These latter two hormones stimulate the testis to synthesise testosterone.
So, testosterone is food to the prostate. Thus food to prostate cancer as well. Hormone therapy, in simple terms, causes castration (removal of testicles) by starving the cancer of testosterone, resulting in death of cancer cells and regression of disease.
When is hormone therapy used?
- In the curative setting of prostate cancer as an addition to other modalities in the intermediate-and high-risk groups.
- Before radiation to shrink the prostate cancer.
- For metastatic cancers as long-term therapy to control and lower disease burden.
- When cancer comes back after initial curative treatment (recurrence).
- It can be used alone in the low-risk setting, or in patients who decline other forms of therapy.
Types of castration
Surgical castration (orchiectomy) is the surgical removal of the testes to eliminate testosterone levels. This method is irreversible.
Chemical or medical castration is the use of drugs to lower testosterone levels. This method, known as hormone therapy, is reversible.
Even though hormone therapy costs more than an orchiectomy and requires more frequent doctor visits, most men choose it. With these drugs, the testicles remain in place, but will shrink over time, and may even become too small to feel.
How do you take hormonal therapy?
The choice of hormone therapy is dependent on factors, such as aims of treatment; stage of disease; and patient factors, like co-morbidities, convenience, compliance and follow-up, etc.
Hormone therapy works peripherally on androgen receptors in tissue (antiandrogens oral tablets) and centrally on the brain (LHRH agonist and antagonist injections).
The injectable drugs are given monthly (agonist and antagonist) or three-monthly (agonist). These can come in the form of pellets or fluid that are injected under the skin.
Antiandrogens are oral tablets that work on the testes and prostate, decreasing the testosterone level. Depending on their risk profile, patients will be given six-month treatment (intermediate-risk), or it could be for two to three years (high-risk), or for the rest of the patient’s life (metastatic).
In the next issue, Dr Ngidi goes into more detail regarding the three types of hormone therapy, LHRH agonists and antagonists,and antiandrogens, and their side effects.
MEET OUR EXPERT – Dr Sithembile Ngidi
Dr Sithembile Ngidi is a clinical and radiation oncologist in Johannesburg. She is passionate about prostate cancer. She is also an honorary lecture at the University of Kwa-Zulu Natal and provides teaching support to registers in radiation oncology at Charlotte Maxeke Johannesburg Academic Hospital.