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Could the 5α-reductase inhibitors (5ARIs) dutasteride and finasteride increase the risk of developing male breast cancer?

In 2012, male breast cancer was identified as a possible new risk of 5ARIs by the FDA; however, a 2013 study published in the Journal of Urology ((Bird ST, Brophy JM, Hartzema AG, Delaney JA, Etminan M. Male breast cancer and 5α-reductase inhibitors finasteride and dutasteride. J Urol. 2013 Nov;190(5):1811-4. doi: 10.1016/j.juro.2013.04.132.)) found no evidence for a relationship between male breast cancer and finasteride (Proscar®) and dutasteride (Avodart®), both of which are used to treat enlarged prostate (benign prostatic hyperplasia).

The study excluded finasteride (Propecia®), used to treat androgenic alopecia, because previous research considered a relationship between Propecia 1mg and male breast cancer unlikely.

So how did dutasteride and finasteride become implicated in the possible development of male breast cancer?

The Hypothesized Link Between Finasteride & Dutasteride and Male Brest Cancer

Going back to 1992, researchers ((Thomas DB, Jimenez LM, McTiernan A, Rosenblatt K, Stalsberg H, Stemhagen A, Thompson WD, Curnen MG, Satariano W, Austin DF. Breast cancer in men: risk factors with hormonal implications. Am J Epidemiol. 1992 Apr 1;135(7):734-48.)) had hypothesized that an increased ratio of estrogen-to-testosterone could lead to an increase risk of male breast cancer.

This hypothesis seemed to be supported when, in 2009, the Medicines and Health care products Regulatory Agency (MHRA) in England ((Niraj K Shenoy, Sangolli M Prabhakar. Finasteride and male breast cancer: Does the MHRA report show a link? J Cutan Aesthet Surg 2010; 3: 102.)) received reports of male breast cancer developing in patients using 5ARIs, which are known to alter the normal estrogen/testosterone balance. Specifically, as of November 2009, MHRA had received 50 worldwide reports of male breast cancer developing within an average of 44 months after starting treatment with 5mg finasteride for enlarged prostate. MHRA also received three reports of male breast cancer developing in men using Propecia ® 1 mg for hair loss, but because of relatively short onset times of the disease after starting treatment, the MHRA considered any link between Propecia and male breast cancer unlikely.

Even though both finasteride and dutasteride alter the normal estrogen/testosterone balance in men, the fact that 50 individuals developed male breast cancer after starting to use a 5ARI does not constitute evidence that 5ARIs contribute to the development of male breast cancer: it is possible that these 50 individuals would have developed cancer whether or not they used a 5a-reductase inhibitor.

The Study: Male Breast Cancer and 5a-Reductase Inhibitors Finasteride and Dutasteride

To ascertain whether or not a link exists between the use of 5a-reductase inhibitors and subsequent development of male breast cancer, one would want to look at two groups of men where one group has been exposed to a 5a-reductase inhibitor and where one group has not, and then one would compare the incidence of the development of breast cancer in the two groups. However, one would also need the two groups to be matched on as many known risk factors for male breast cancer as possible, such as alcoholism, gynecomastia, Klinefelter syndrome, liver damage, obesity, oral estrogen, orchiectomy and prior radiation; in short, one would want to control for all the known risk factors for male breast cancer to see if 5ARIs were contributing any additional risk.

And this is exactly what the 2013 study did. As a result, it found that 5a-reductase inhibitors were not a significant predictor of developing male breast cancer 1 to 3 years after exposure.

Because no link between 5ARIs and male breast cancer was found, the authors of the study advised doctors to prescribe finasteride and dutasteride without fear of introducing additional risk for the development of male breast cancer in their patients.

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Q: I’ve heard that FDA added a description of reports of male infertility to the side effect labels of both Propecia and Proscar (finasteride). Is this a likely side effect in your experience? — S.S., Rolling Hills, California

A: Propecia (finasteride 1mg) may lead to male infertility not only by changing the consistency of the male ejaculate but by decreasing the sperm count as well, but this is uncommon.

Ejaculate is a combination of sperm produced by the testes and a viscous fluid made by the prostate. Since finasteride shrinks the prostate, it can make the ejaculate less viscous (more watery).

Most patients trying to conceive will have no issues while taking Propecia.

If one is having difficulty trying to conceive for 4-6 months, then it is reasonable to stop taking Propecia.

It is important to know that taking Propecia while trying to conceive will not lead to congenital deformities or issues with the fetus as long as the woman does not come in direct contact with the medication.

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Q: I have heard that side effects from finasteride can persist even after stopping the medication. What is the most current information on this issue? — S.V., Short Hills, N.J.

A: For the past two years I have been on the International Society for Hair Restoration Surgery (ISHRS) Task Force on Finasteride Adverse Events and struggling to make sense of this issue. There seems to be a disconnect between the relatively low incidence of side effects that we, as physicians, see in our practices, what published controlled studies have shown, and what is now being reported on the internet and in some instances in the media. For example, a 2012 study by Sato of 3,177 Japanese men published the Journal of Dermatology, showed a 0.7% incidence of adverse reactions to finasteride 1mg and no persistent side effects after stopping the medication.

That said, there has been a recent increase in anecdotal reports of side effects from finasteride as well as reports of persistent side effects after the medication has been discontinued (referred to as “Post-finasteride Syndrome”).

The FDA

Based on post-marketing reports of sexual dysfunction, in April 2012, the FDA announced changes to Propecia (finasteride 1 mg) labeling to expand the list of sexual adverse events and that some of these events had been reported to continue after the drug is no longer being used. It is important to note that no new clinical studies were reviewed to evaluate these adverse events and that the FDA is not aware of any additional controlled clinical studies conducted to evaluate these adverse events or to determine their cause or duration. (see FDA Label Changes for Finasteride 2012)

The FDA states that despite the fact that clear causal links between finasteride (Propecia and Proscar) and sexual adverse events have NOT been established, the cases suggest a broader range of adverse effects than previously reported in patients taking these drugs. The FDA states that it believes that finasteride remains a safe and effective drug for its approved indications, but also advises that healthcare professionals and patients should consider this new label information when deciding the best treatment option.

The difficulty with interpreting anecdotal information is significant. The following need to be considered; first, sexual dysfunction, both temporary and persistent, is quite common in the general population and patients may have new-onset sexual dysfunction from some other, unrelated, cause and second, patients may have real (physiologic) side effects from the medication and then have psychological after effects. It is so difficult to sort these factors out.

The ISHRS

The Finasteride Symposium at the 2012 ISHRS, of which I was a panelist, explored safety issues with finasteride. Dr. Akio Sato presented his data (quoted above) suggesting that finasteride side effects are uncommon and that persistent side effects were not seen. Dr. Freedland, a urologist and featured guest speaker at the ISHRS symposium, questioned whether long-term effects of a slight elevation in estrogen levels could have adverse effects on the prostate. The panel discussed the paper of Dr. Michael Irwig at George Washington University that appeared in The Journal of Sexual Medicine this year. In his survey of 54 patients of men who had persistent sexual side effects three or more months after the discontinuation of finasteride, he reported that sexual dysfunction continued for many months or years in the majority of the patients.

Difficulties in interpreting this study are that it assumed that the patient’s sexual dysfunction were caused by finasteride when, in fact, there is no way of knowing that finasteride was the actual cause of the side effects (this would need a blinded, placebo-controlled study). A second reason that makes interpretation difficult is that, because there was selection bias in the Irwig survey, there is no way of knowing if these patients are representative of the population of men on finasteride. That said, the data presented by Dr. Irwig stresses the importance of having more clarity on the potential side effects of finasteride, since it is so widely prescribed.

It was clear from the presentations and questions asked, that many issues are still unresolved. All in attendance agreed that further research is urgently needed. In the short term, it is most important that all patients who are having problems can have easy access to doctors with expertise in this area, so that they can be diagnosed properly and treated.

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On April 11, 2012, the U.S. Food and Drug Administration (FDA) announced changes to the professional labels for Propecia (finasteride 1 mg) and Proscar (finasteride 5 mg) to expand the list of sexual adverse events reported to FDA as some of these events have been reported to continue after the drug is no longer being used (note that erectile dysfunction after stopping use of these drugs was added as a known event in 2011). The new label changes include:

  • A revision to the Propecia label to include libido disorders, ejaculation disorders, and orgasm disorders that continued after discontinuation of the drug.
  • A revision to the Proscar label to include decreased libido that continued after discontinuation of the drug.
  • A revision to both the Propecia and Proscar labels to include a description of reports of male infertility and/or poor semen quality that normalized or improved after drug discontinuation.

Despite the fact that clear causal links between finasteride (Propecia and Proscar) and sexual adverse events have NOT been established, the cases suggest a broader range of adverse effects than previously reported in patients taking these drugs.

Propecia

Only a small percentage of men using these drugs have experienced a sexual adverse event. During treatment with Propecia, 3.8% of men had reported one or more adverse sexual experiences as compared to 2.1% men who did not receive Propecia (received placebo). This represents a 1.7% difference.

For Propecia, the FDA’s Agency’s Adverse Events Reporting System (AERS) database between 1998 and 2011 found 59 cases of reported sexual dysfunction that lasted for at least three months following discontinuation of Propecia, and included erectile dysfunction, decreased libido, problems with ejaculation and orgasm disorders.

The FDA has not established a cause and effect relationship between finasteride and the sexual adverse events that continued after stopping drug use. The FDA believes that finasteride remains a safe and effective drug for its approved indications. Healthcare professionals and patients should consider this new label information when deciding the best treatment option.

For more information, read this PDF document: Questions and Answers: Finasteride Label Changes.

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Q: Are there DHT blockers that are sold in the pharmacy over the counter? — C.C., — Fairfield County, Connecticut

A: The only effective DHT blockers are finasteride (Propecia, Proscar) and dutasteride (Avodart).

These medications require a doctor’s prescription and are not sold OTC. Nizoral is a topical shampoo for seborrhea (a type of dandruff) that is sold over the counter, but it is not effective in treating hair loss.

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Q: I have been using Propecia since it was released to the public in 1998 and have found it to work very well. Recently, its effectiveness has stopped and my hairs are miniaturizing again. I am going to increase the dosage to 1/2 a pill Proscar every day. How long will the increased dosage take to stop the miniaturizing process? — T.U., Chappaqua, N.Y.

A: It seems to take the same time to work as when you initially started Propecia.

When patients increase their dose, I rarely see re-growth, but rather the expectation is that further hair loss will be decreased. When it does work to actually re-grow hair, we sometimes see an initial period of shedding, similar to when finasteride was first started.

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Q: Will Propecia and Minoxidil reverse some of the miniaturization going on with someone with thinning hair? If I do need a hair transplant will I have to stay on these medications? — C.C., — Fairfield County, Connecticut

A: Yes, both minoxidil (Rogaine) and finasteride (Propecia, Proscar) affect the miniaturization of the hair follicles and help restore the shrunken follicles to cosmetically viable hair.

Minoxidil works by directly simulating miniaturized follicles to grow, whereas finasteride blocks DHT, the hormone that causes hair to miniaturize and eventually fall out.

Finasteride is much more effective than minoxidil in preventing or reversing the miniaturization process and it is so much more convenient to use that we generally suggest finasteride after a hair transplant procedure, but rarely recommend minoxidil.

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Q: My friend is taking Avodart, he bought it over the internet. Is it safe to take? — T.G., Denver, Colorado

A: Avodart (dutasteride 0.5mg) was approved by the FDA for the treatment of prostate enlargement in men in 2002. Avodart has not been approved for the treatment of androgenetic hair loss, although physicians can use an approved medication in ways other than for which it was specifically approved. That said, the use of dutasteride certainly requires a doctor’s supervision.

Like finasteride (the active ingredient in Proscar and Propecia), dutasteride blocks the enzyme 5-alpha reductase that converts testosterone to DHT (DHT is a key hormone that causes hair loss). However, unlike finasteride, which only inhibits the Type I form of the enzyme, dutasteride inhibits both the Type I and Type II forms. This combined effect lowers circulating DHT more with dutasteride than with finasteride, but also increases the incidence of its side effects.

The Type II form of the enzyme (blocked by finasteride) is found predominantly in the hair follicle. The Type I form of the enzyme has been found in the scalp and sebaceous glands, and many other parts of the body, but its exact role in hair growth has not been determined. It is felt that dutasteride’s ability to dramatically lower serum levels of DHT is what makes it a more potent medication in hair loss.

When considering the safety of dutasteride, one should consider the following:

  • It acts on other parts of the body besides the hair follicle.
  • Unlike finasteride, where families that had a deficiency of the Type II 5-alpha reductase enzyme were followed for years without any adverse effects, there is no natural biologic model to show the safety of dutasteride.
  • Dutasteride has been approved for prostate enlargement in an older male population. It is not approved for hair loss and, in fact, the clinical trials for hair loss were discontinued, so there is no safety data for its use in younger patients. There is a greater incidence of sexual side effects with dutasteride compared to finasteride.
  • The 1/2 life of dutasteride is 5 weeks compared to 6-8 hours for finasteride. Serum concentrations of dutasteride are detectable up to 4-6 months after discontinuation of treatment.
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Q: I heard that Propecia was being used originally for shrinking the prostate, is this true? — M.D., New Hyde Park, N.Y.

A: Propecia (finasteride 1mg) is not a prostate medication that was serendipitously noted to have a side effect of re-growing hair, it is a medication that was known all along that it might be able to slow hair loss and/or to grow hair.

Although finasteride was first approved for the treatment of prostate enlargement, the researchers at Merck knew, at the outset, that there were families whose members were deficient in the 5-alpha reductase Type II enzyme and that the men in these families neither developed prostate disease nor went bald. In addition they had no long-term problems from the lack of this enzyme.

Merck used this natural model to develop a medication that could block the 5-alpha reductase Type II enzyme – the result was finasteride. Because the only approved treatment for symptoms related to prostate enlargement at the time was surgery, Merck developed finasteride as a medical treatment for this condition prior to developing finasteride as a potential treatment for men with male pattern hair loss.

This also meant that Merck would understand the safety profile of finasteride, and have it approved for a medical disease (symptomatic prostate enlargement), before developing it for a cosmetic condition.

The drug was first submitted to the FDA for the treatment of prostate enlargement as Proscar (finasteride 5mg) in 1991 and it was approved for this use in 1992. The drug was submitted for the treatment of men with male pattern hair loss as Propecia (finasteride 1mg) in 1996 and was approved for this use in 1997.

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Q: I heard that Proscar, the 5mg version of finasteride, is now generic. Is that correct and is Propecia going generic as well? — F.J., Red Hook, Brooklyn, NYC

A: Yes, Finasteride 5mg (Proscar) is now available in a generic formulation. It is my understanding that Finasteride 1mg (Propecia) will not be available generically until the year 2012.

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Q: I am currently taking Propecia 1mg a day for hair loss and heard that Proscar 5mg now comes in a generic form. If I get that, how should I take it? — G.A., Fort Lauderdale, FL

A: If you are currently taking Propecia 1mg a day, and want to switch to Proscar (Finasteride 5mg), you can either take Proscar 5mg, 1/4 pill every day or 1/2 pill every other day.

If you break up the pills, be mindful of the potential risk to pregnant women from handling crushed tablets. You can purchase a pill cutter in any pharmacy.

You should be aware that this dosing is not recommended by Merck and that there are no studies showing that either breaking up the pills or taking alternate day dosing is as effective as taking Propecia (Finasteride 1mg) a day.

That said, finasteride lasts in tissues for several days, so these alternate day dosing schedules seem reasonable.

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Q: I recently turned 22 and have been on Propecia for about 2.5 years. The amount of hair that de-miniaturized with daily 1 mg peaked about a year ago and I have seen steady thinning since. I feel that I am too young for a hair transplant. My question is whether or not an increase in dosage of Propecia is indicated here or if I should seek other options entirely? — N.W., Portland, Oregon

A: At 22 years old, I would increase the dose of Propecia before considering hair restoration surgery. However, it is important to realize that there is no scientific evidence that increasing the dose will have any additional effects. There are published data by Roberts et al in the JAAD in 1999 demonstrating that 5 mg is no better than 1 mg from controlled clinical trials.

I usually increase the dose when someone has been on the same dose of medication for about three years, although there is no good data on how exactly to increase the dose, or that it will actually make a difference.

For this purpose, I generally use finasteride in the form of Proscar 5mg every other day (or Proscar 1/2 pill every day).

If you break up the pills, be mindful of the potential risk to pregnant women from handling crushed tablets.

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