Fluoxymesterone (Halotestin) and the Prostate: What the Research Says

The prostate is an androgen-dependent organ, so the question of how fluoxymesterone (Halotestin) affects it is entirely natural. At the same time, the topic has become surrounded by both scare stories and unfounded complacency. Our editorial team has examined what research says about androgens and the prostate, what exactly is written in the drug's package insert, and which examinations make sense for men of different ages.

The prostate as an androgen-dependent organ

The prostate gland develops and maintains its function under the influence of androgens. The main active hormone in its tissue is dihydrotestosterone, formed from testosterone by the enzyme 5α-reductase type 2. Men with a congenital deficiency of this enzyme have an underdeveloped prostate, a classic example of how much the gland depends on the androgen signal.

In adulthood, androgens regulate the growth of gland cells, the production of secretions and the synthesis of prostate-specific antigen (PSA). Castration or medical suppression of androgens reduces prostate volume, and it is precisely on this principle that the hormonal treatment of prostate cancer is based.

Fluoxymesterone acts as a strong agonist of the androgen receptor. It does not aromatize into estradiol but, according to pharmacological data, may be partly metabolized into 5α-reduced derivatives. Practically important is that its effect on the prostate is mediated by the same receptor as the effect of the body's own androgens.

There are no direct clinical studies examining the effect of fluoxymesterone on prostate volume, PSA or cancer risk. Therefore conclusions are based on general data about androgens, on the drug's package insert and on the results of testosterone studies.

What the package insert says

The package insert for Halotestin contains clear contraindications: the drug must not be used in men with established or suspected prostate cancer and breast cancer. The reason is simple, androgens can stimulate the growth of androgen-sensitive tumors.

The insert also warns that in older men androgens may increase the risk of prostate hypertrophy and prostate cancer. Particular caution and medical monitoring are provided for this group.

These provisions apply to medical doses, which are considerably lower than those encountered in non-medical use. It is logical to assume that at supraphysiological doses the androgenic stimulation of the prostate will be no less, although quantitative data for fluoxymesterone are lacking.

It is worth mentioning separately that fluoxymesterone was used in oncology, but for the palliative treatment of breast cancer in women, not for treating male tumors. It has no oncological indications regarding the prostate.

Benign hyperplasia and urinary symptoms

Benign prostatic hyperplasia (BPH) is an age-related enlargement of the prostate that can compress the urethra. It manifests as a weak stream, frequent urges, nighttime urination and a feeling of incomplete emptying. The development of BPH depends on androgens: without them the gland does not enlarge.

Evidence of the role of androgens is the effectiveness of 5α-reductase inhibitors (finasteride, dutasteride), which reduce prostate volume and relieve symptoms. The logic is the reverse: an excess of androgenic stimulation may theoretically accelerate gland growth and worsen symptoms.

For testosterone replacement therapy at physiological doses, large studies have not shown significant worsening of symptoms in most men; however, the Endocrine Society guidelines (2018) advise against starting therapy in men with severe lower urinary tract symptoms without a urologist's assessment. For supraphysiological doses of strong androgens there are no such reassuring data.

If, on the background of any androgens, difficult urination, frequent nighttime urges or urinary retention appears, that is a reason to see a urologist. Acute urinary retention is an emergency.

Prostate cancer: from classic views to the saturation model

The classic view, formed back in the mid-20th century, was that androgens «feed» prostate cancer and that lowering them restrains the tumor. It still underlies androgen-deprivation therapy for advanced cancer.

Morgentaler and Traish (2009) proposed the saturation model: the androgen receptors of the prostate become saturated already at relatively low androgen concentrations, so raising the hormone level above this threshold has little effect on tissue growth. This model explains why replacement therapy within the physiological range has not shown a clear increase in cancer risk in studies.

However, the saturation model applies to testosterone within physiological fluctuations and is not a «license» for supraphysiological doses of strong synthetic androgens. For such situations the data are insufficient, and no one has repealed the contraindications in the package insert.

An interesting indirect argument is the PCPT study (Thompson et al., 2003), in which finasteride reduced the overall detection rate of prostate cancer by roughly a quarter. This underscores that androgenic stimulation is indeed linked to the development of prostate cancer, although the link is complex and depends on the type of tumor.

PSA and urological monitoring

Prostate-specific antigen is a protein produced by prostate cells. Its level in the blood rises with cancer, but also with BPH, prostatitis, after ejaculation, cycling or urological procedures. Androgens themselves stimulate PSA synthesis, so while taking them the value may rise without a tumor.

The Endocrine Society guidelines on testosterone therapy recommend assessing prostate cancer risk and PSA before starting treatment in men of the appropriate age and monitoring it over time. The logic of monitoring is this: not only the level matters, but also its rate of rise.

Practical rules for a PSA test:

• refrain from ejaculation and cycling loads for 48 hours before the test;
• do not take the test during a urinary tract infection flare-up;
• compare results from a single laboratory, since methods may differ;
• discuss the result with a urologist rather than judging it yourself against the «norm» on the form.

For young men without symptoms, routine PSA screening is usually not recommended. But if an older man is using or has used androgens, urological examination becomes much more appropriate.

Editorial conclusions

The prostate depends on androgens, and fluoxymesterone, as a strong androgen-receptor agonist, is capable of affecting it. The package insert directly contraindicates the drug in prostate cancer and requires caution in older men.

The saturation model explains the safety of physiological replacement therapy, but it does not automatically extend to supraphysiological doses of synthetic androgens, here the data are simply lacking.

Urinary symptoms, a rising PSA or an age over 40–50 years are strong grounds for consulting a urologist.

We also recommend reading our materials on how to properly have a PSA test, on the effect of fluoxymesterone on fertility, and on the tests for monitoring while using androgens.

References

1. Morgentaler A, Traish AM. Shifting the paradigm of testosterone and prostate cancer: the saturation model and the limits of androgen-dependent growth. Eur Urol. 2009;55(2):310–320.
2. Thompson IM, Goodman PJ, Tangen CM, et al. The influence of finasteride on the development of prostate cancer. N Engl J Med. 2003;349(3):215–224.
3. Bhasin S, Brito JP, Cunningham GR, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103(5):1715–1744.
4. Halotestin (fluoxymesterone tablets, USP). Prescribing information. Pharmacia & Upjohn.
5. Pope HG Jr, Wood RI, Rogol A, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341–375.
6. Nieschlag E, Behre HM, Nieschlag S (eds). Testosterone: Action, Deficiency, Substitution. 4th ed. Cambridge University Press; 2012.