Top
Man having a discussion with a medical doctor.

Viagra and Cancer: Frequently Asked Questions

We’ve previously written about the facts and fiction around drugs like Viagra and Cialis, both popular medications used to treat erectile dysfunction. In this article, we’ll take a closer look at the relationship (or lack thereof) between Viagra and colorectal cancer, melanoma, and prostate cancer. If you find this article helpful, visit eDrugstore.com’s blog for more like it. 

People spend a lot of time talking and thinking about the nearly infinite number of things that cause cancer, and for good reason: Although the annual mortality rate has steadily declined over the past decade, cancer remains the second leading cause of death in the United States after heart disease.1 Almost all of us have been affected by this disease in some way or another, whether from our own personal experience or the struggle, survival, and loss of family and friends.

Scary stuff, and one of the scariest parts is that there isn’t usually a specific cause you can seek out and eliminate. That’s because cancer tends to result from the influence of many different factors over time that produce genetic mutations that let cells grow out of control. It’s getting harder and much more expensive to develop new cancer drugs, and scientists and drug companies have started looking for unrecognized anti-cancer potential in drugs already in use, sometimes for completely unrelated purposes.2

Like Viagra, for example!

Viagra + Cancer = Is There a Connection?

“Wait,” you say. “Viagra? Like, the blue erection pills? What’s that have to do with cancer?”

The very same. You might be surprised to learn that Viagra, or sildenafil, wasn’t always a blockbuster ED drug. It started humbly, originally being tested as a treatment for high blood pressure and chest pain when male study participants taking the medication started reporting frequent and unexpected erections (statistically the least-enjoyable type of erection12).

When researchers concluded that Viagra is much more effective at causing erections than it ever was at reducing chest pain, it was repurposed as the first erectile dysfunction treatment you can take by mouth.

A growing body of scientific research is revealing another opportunity to repurpose Viagra, this time as a potential adjunct cancer drug that may improve survival, reduce the chance of cancer spreading, and boost the effectiveness of chemotherapy regimens. Given the enormous spike in the number of men taking the drug starting in the early 2000’s, there have also been some concerns about whether it can increase or decrease your risk of certain cancers in the long term.

How Viagra Works

Before we jump into the details, let’s review how drugs like Viagra work, because it’s related to their potential anti- or pro-cancer activity.

When men get sexually aroused, a chemical called cGMP is released and causes the blood vessels that supply the penis to open up and allow more blood to flow in. As the penis fills with blood, it hardens and compresses the outgoing veins to prevent the blood from leaving.

When the sexual stimulus goes away, an enzyme called phosphodiesterase-5 (PDE5) breaks down the cGMP. This lets the arteries that supply the penis shrink back to their original size so less blood flows in and the trapped blood drains out.

Viagra and other drugs like Cialis and Levitra are PDE5 inhibitors, or PDE5is. They attach to the PDE5 enzyme and stop it from breaking down cGMP. This allows cGMP to stick around longer and continue exerting its effects on blood flow to the penis, which makes it much easier to get and maintain an erection.

Cancer Research in a Nutshell

Viagra has been investigated for both direct effects on cancer cells and for indirect positive and negative influences on cancer formation, metastasis (spreading), and recurrence. To examine the direct effects of any drug on tumor cells, scientists often start with smaller-scale studies using mouse and human cancer cell lines, which are just samples of cells of a specific cancer type that can be replicated and grown in a lab.

Lab scientist reading documents.

Cancer cell lines are useful for identifying drugs that have potential anti-cancer or pro-cancer effects because researchers can use them to quickly grow a large sample of cancerous cells with the same mutations and then test many drugs one-after-another. Drugs that appear to shrink or prevent tumors in these laboratory studies can then be investigated in live animals and eventually in clinical trials in humans.

When it comes to doing cancer trials in humans, there are a lot of things we want to know, but each thing by itself isn’t significant enough to justify the amount of money a full randomized clinical trial costs. In these cases, researchers often rely on cohort studies where they look at the data collected from large patient groups to identify possible patterns and trends, usually guided by the results found in the lab. Most of the studies we’ll be discussing in the next few sections are cohort-type studies.

Can Viagra Lower my Risk of Getting Colon Cancer?

Verdict: Viagra appears to lower the risk of colorectal cancer recurring and spreading after colon-removal surgery. However, the evidence doesn’t point to any relationship between using Viagra and your likelihood of developing colon cancer if you’ve never had it before. 

Hands holding a small and large intestine model.

One area where PDE5i drugs may have some benefit is in colorectal cancer (CRC). CRC is the third most common cancer and the third leading cause of cancer-related death in the United States.3 The preferred initial treatment after diagnosis is surgical removal of part or all of the large intestine, a procedure known as a bowel resection. This is done either through a large incision in the abdominal area (an “open” surgery) or laparoscopically through several smaller incisions.

Unfortunately, there is growing evidence suggesting the surgery may increase the risk that the cancer will spread, especially in patients undergoing the more invasive open surgery.4,5 The added risk is thought to result from the way that cancer and major surgery affect the immune system, where the killer T cells that otherwise destroy cancer get suppressed by other immune cells that aren’t working right. With these defenses lowered, tumor cells that break off during the resection have easier time putting down roots in a new location.

Experiments using mouse and human CRC cell lines suggest that sildenafil may help prevent tumors from forming or spreading by correcting the immune suppression and restoring those cancer-killing T cells to their previously lethal selves.4

In one set of studies, scientists used mice that were modified with a human gene mutation that causes familial adenomatous polyposis, or FAP, a condition where a patient’s bowel produces hundreds and hundreds of polyps and almost always results in colorectal cancer at a young age.

Giving a low dose of Viagra to the mice had no effect on already existing polyps, but it cut the number of new polyps formed in half.6 In a related study, a different mouse model of colitis (chronic inflammation of the colon) showed a 50% reduction in new polyp formation after being treated with Viagra.6

DNA strand.

A team at Lund University in Sweden took this a few steps further to determine what these findings meant for human cancer patients. They analyzed the Swedish Cancer Registry database to identify patients with colorectal cancer, compare their genetic profiles, and determine their use of Viagra or other PDE5is before and after surgical bowel resection. They found that patients with higher levels of the gene for PDE5 had significantly lower rates of survival in comparison to patients with lower levels of this gene.

So what does that mean? It means that having too much PDE5 activity plays a role in CRC progression, and that drugs that block PDE5 may improve the likelihood of survival.

The authors reported that patients who used PDE5is after being diagnosed with CRC had a significantly lower risk of CRC-related death as well as a reduced risk of their cancer spreading. The anti-cancer effect was especially strong when PDE5is were used post-operatively after bowel resection, and even more so if the patient underwent the more invasive open surgical procedure.5

This is probably the most solid evidence of Viagra’s potential usefulness as an add-on to chemotherapy, but the benefit may be limited to patients who already have CRC and are having surgery to remove it. Hopefully, future clinical trials will help to clarify and focus whether Viagra can reduce the risk of colon cancer in men who haven’t had cancer before.

Does Viagra Cause Melanoma?

Verdict: Despite the scary sounding numbers, there isn’t really any evidence to suggest there is anything more than a slight association between Viagra and an increased risk of melanoma. There is no evidence that Viagra or other PDE5i drugs cause melanoma or any other cancer.

Man with a sun and waves on his back.

The concern that Viagra may increase the risk and severity of the skin cancer melanoma sprang up from lab research into how Viagra affects the signals that cells use to communicate with each other.

Researchers noticed that the erectile dysfunction drug works by a similar mechanism that melanoma cells use to break away from the tumor and spread to the rest of the body—by blocking the PDE5 enzyme. The difference is that Viagra blocks PDE5 that’s already there, while in melanoma a gene mutation causes less PDE5 to be made to begin with.7

This isn’t an outrageous idea, because PDE5 is found all over the body, not just the penis. Since Viagra gets carried all over by the bloodstream, it can bind to PDE5 in other areas as well, with the potential for undesired effects. Several groups of researchers have tried to determine if this theory is a real cause for concern and if so, what role Viagra actually plays in it.

A study published in the Journal of the American Medical Association: Internal Medicine analyzed a large database of survey responses from nearly 26,000 men participating in the Health Professionals’ Follow-Up Study. They found that men who took Viagra were 84% more likely to develop melanoma than men who had never taken it.7

At face value, that certainly sounds terrifying, but it’s important to realize that the 84% figure is the relative increase in risk between the two groups. The actual, or absolute risk, in either group is still very low, but the relative numbers are often reported to make an association seem more significant than it really is. Importantly, the authors of this study emphasized that their results didn’t show that Viagra was the cause of the increased risk, just that using Viagra was associated with an increased risk of melanoma.7

Other researchers have tried to verify the results from the above one. Most concluded either no association existed or that there may be a slight association between melanoma and Viagra use, but it’s nowhere near significant enough to stop using PDE5i drugs to manage erectile dysfunction.8,9

Medical doctor looking at a patient's skin.

What multiple sources DO confirm though, is that sun exposure is by far the greatest contributor to your risk of developing invasive melanoma. If you want to decrease your risk of getting the deadliest of the skin cancers, limit your sun exposure, check moles on your skin regularly, and protect your skin with clothing and sunscreen when you can’t stay out of the sun. These tips will get you a lot farther than tossing your Viagra prescription in the trash would.

Of course, if you panicked and already threw your script out, eDrugstore.com can connect you to a licensed telehealth doctor to get a new one, and even ship it right to your doorstep for no extra charge.

Will Viagra Increase My Risk of Getting Prostate Cancer?

Verdict: There’s little evidence to show taking Viagra or other PDE5i drugs increases your risk of getting prostate cancer if you’ve never had it, or of your prostate cancer recurring if you have. Experts advise clinicians and patients to continue using these drugs to manage erectile dysfunction as they always have.

A study done in Germany in 2014 reported an association between Viagra and the recurrence of prostate cancer in men who had already had surgery to remove the cancer, a procedure called a radical prostatectomy. This was an unexpected result, completely opposite of what the researchers had anticipated. But like the other database-review type studies we’ve looked at in this article, it’s important to remember that results that show an association between two things don’t necessarily show that one causes the other.

In this case, the association was probably because the men with more aggressive cancer often require more invasive surgery to remove it. This is much more likely to damage nerves and blood vessels around the prostate and result in erectile dysfunction. So the men who required ED drugs may have already had more invasive, aggressive cancer that is more likely to recur than the men not taking ED drugs after prostatectomy.

More comprehensive studies done since then have confirmed that use of a PDE5i drug to treat erectile dysfunction after prostate cancer surgery does not appear to increase the risk of the cancer recurring, and clinicians and patients can continue to use them to manage ED without cause for alarm.10,11

Hand with a blue ribbon.

Wrap-Up

Hopefully this article has shown you that figuring out the long-term effects of a particular drug can be difficult, even for the experts. What isn’t difficult though, is getting treatment for erectile dysfunction through a dedicate telehealth provider like eDrugstore.com. Click here to browse our inventory and learn more about the process.

References

 

1. Centers for Disease Control and Prevention. Leading causes of death. 2017. https://www.cdc.gov/nchs/fastats/leading-causes-of-death.htm. Accessed 8/23/2020.

2. Pantziarka P, Sukhatme V, Crispino S, Bouche G, Meheus L, Sukhatme VP. Repurposing drugs in oncology (ReDO)-selective PDE5 inhibitors as anti-cancer agents. Ecancermedicalscience. 2018;12:824. Published 2018 Apr 11. doi:10.3332/ecancer.2018.824

3. Siegel, R. L., Miller, K. D. & Jemal, A. Cancer statistics, 2019. CA Cancer J. Clin. 69, 7–34 (2019).

4. Neeman, E. & Ben-Eliyahu, S. Surgery and stress promote cancer metastasis: new outlooks on perioperative mediating mechanisms and immune involvement. Brain Behav. Immun. 30, S32–S40 (2013).

5. Huang, W., Sundquist, J., Sundquist, K. et al. Phosphodiesterase-5 inhibitors use and risk for mortality and metastases among male patients with colorectal cancer. Nat Commun 11, 3191 (2020). https://doi.org/10.1038/s41467-020-17028-4

6. Medical College of Georgia at Augusta University. “A small, daily dose of Viagra may reduce colorectal cancer risk.” ScienceDaily. ScienceDaily, 19 March 2018. <www.sciencedaily.com/releases/2018/03/180319090653.htm>.

7. Li W, Qureshi AA, Robinson KC, Han J. Sildenafil Use and Increased Risk of Incident Melanoma in US Men: A Prospective Cohort Study. JAMA Intern Med. 2014;174(6):964–970. doi:10.1001/jamainternmed.2014.594

8. Loeb S, Ventimiglia E, Salonia A, Folkvaljon Y, Stattin P. Meta-Analysis of the Association Between Phosphodiesterase Inhibitors (PDE5Is) and Risk of Melanoma. J Natl Cancer Inst. 2017;109(8):djx086. doi:10.1093/jnci/djx086 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5437700/

9. Shkolyar E, Li S, Tang J, Eisenberg ML. Risk of Melanoma With Phosphodiesterase Type 5 Inhibitor Use Among Patients With Erectile Dysfunction, Pulmonary Hypertension, and Lower Urinary Tract Symptoms. J Sex Med. 2018;15(7):982-989. doi:10.1016/j.jsxm.2018.05.002 https://pubmed.ncbi.nlm.nih.gov/29884444/

10. Susman, Ed No Let Down, Oncology Times: February 25, 2016 – Volume 38 – Issue 4 – p 15 doi: 10.1097/01.COT.0000481197.70486.46

11. Jamnagerwalla J, Howard LE, Vidal AC, et al. The Association between Phosphodiesterase Type 5 Inhibitors and Prostate Cancer: Results from the REDUCE Study. Volume 196 – Issue 3 – September 2016 – Page: 715-720. https://doi.org/10.1016/j.juro.2016.03.172

12. OK, we don’t actually have stats to back that one up, but it seems pretty plausible, doesn’t it?

Randall is a medical writer with years of experience in the healthcare and pharmaceutical industries. After earning his Doctor of Pharmacy degree from the Albany College of Pharmacy and Health Sciences, he worked as an infusion and specialty pharmacist, where he discovered his passion for making trustworthy healthcare information accessible to everyone.