Smoking and Breast Cancer: What the Research Shows

Breast cancer is the second most common cancer among women in the U.S. It’s also the second leading cause of cancer deaths. Some risk factors for breast cancer can’t be controlled, like genetics and age. But others can be modified, including lifestyle choices like smoking.

Breast cancer’s relationship with smoking is a little complicated. This may be because many women who smoke also drink alcohol. And we know alcohol consumption is a known risk factor for breast cancer. But recent evidence suggests smoking alone can increase someone’s risk of breast cancer. Let’s dive into the relationship between the two. 

How much does smoking increase your risk of breast cancer?

Older studies show conflicting evidence on how much smoking increases your risk for breast cancer. But more recent studies are pointing to a modest association between the two. People who currently smoke have about a 10% higher chance of having breast cancer than people who have never smoked. 

There’s a greater increase in breast cancer risk in people who have been smoking for longer. The cumulative exposure to cigarette smoke seems to be important. This means the more and longer your smoke, the higher your risk of breast cancer. For example, one large study showed that women had a 35% higher chance of developing breast cancer in their lifetime if they:

• Started smoking more than 5 years before the birth of their first child

• Had a cumulative smoking history of 20 pack-years 

As seen in this study, the timing also matters. The risk of smoking seems to be higher in the years before a woman has her first child. On the flip side, postmenopausal women seem to be less susceptible to the increased breast cancer risk from smoking. The exact mechanism behind this isn’t clear, but it’s likely related to length of exposure to estrogen, which is another risk factor for breast cancer.  

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Smoking and estrogen-receptor positive breast cancer

There’s a subset of breast cancers called estrogen-receptor positive breast cancers (or ER+). These cancer cells have many estrogen receptors, and estrogen makes these tumors grow. A breast cancer’s estrogen receptor status is important because it determines the treatment options. ER+ cancers can be treated with hormone therapies and may have a better survival rate than estrogen-negative tumors. 

Smoking is most likely to increase the chance of an ER+ breast cancer, as opposed to ER negative. Research suggests smokers have a higher risk of developing ER positive breast cancer than people who have never smoked. 

But, for women with ER+ breast cancer, smoking didn’t increase the risk for:

• Metastatic disease

• Recurrence 

So more research is needed to better understand these findings.

Does secondhand smoke also contribute to breast cancer?

The link between breast cancer and secondhand smoke is less clear. Many observational studies haven’t found a link between secondhand smoke and breast cancer. But other large studies have. It’s possible the timing of smoke exposure is a factor, as mentioned above. 

Regardless of what future studies find on secondhand smoke and risk of breast cancer, experts know it has other health effects. Secondhand smoke has been linked to other cancers and respiratory problems in kids. So it’s clear that staying away from secondhand smoke will benefit your overall health.

How does smoking affect breast cancer treatment?

The answer depends on how much you smoked and if you’re still currently smoking. People who smoked over 20 pack-years may have a higher chance of:

• Breast cancer recurrence (the cancer coming back)

• Dying from breast cancer 

The more you smoke, the higher the risks. These risks are also higher if you continue smoking after diagnosis, as opposed to quitting smoking. 

More specifically, people who smoke have a higher chance of:

• Wound-healing complications after surgery: They have about double the chance of a wound complication, like an infection, after mastectomy breast surgery. 

• Complications during radiation treatment for breast cancer: These can include skin reactions in the radiated area, decreased function of the lungs, and getting a secondary cancer. 

• Cancer progression: In the lab, nicotine made breast cancer cells more resistant to doxorubicin, a chemotherapy medication. It seems that nicotine makes cancer cells less likely to die even when treated with chemotherapy. This may lead to a higher chance of breast cancer metastasizing. 

This means smoking after a breast cancer diagnosis doesn’t just affect your survival, it can cause more complications. 

If you quit smoking, can it decrease your risk of breast cancer?

Yes, quitting smoking can decrease your breast cancer risk. The cumulative exposure to smoke is what increases your chance of developing breast cancer. So the sooner you quit smoking, the faster you can decrease your breast cancer risk. And the longer you have quit smoking, the lower your risk becomes. Avoiding cigarette smoke exposure is a recommended way to actually prevent breast cancer. 

It’s not easy, but smoking cessation is also good for many other aspects of your health, like your heart health. If you’re interested in quitting smoking, talk with a healthcare professional about the best way to quit. There are a lot of helpful resources. 

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Written by:

Nicole Andonian, MD

Nicole Andonian, MD, is a private practice anesthesiologist in Orange County, California. Her focus is in general anesthesia, regional anesthesia, and acute pain management.

Edited by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

Reviewed by:

Mandy Armitage, MD

Mandy Armitage, MD, has combined her interests in clinical medicine with her passion for education and content development for many years. She served as medical director for the health technology companies HealthLoop (now Get Well) and Doximity.

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