Breast cancer in men accounts for less than 1% of all breast cancer cases. But because the disease is so common, that still amounts to about 2,000 cases in the United States every year.
To date, little research has been done on male breast cancer, and the current treatments for men with the disease are based on what doctors have learned from treating women. But that is changing, with a comprehensive research program from several leading international breast cancer research groups now under way.
Here is what we know — and what we’re learning — about male breast cancer.
What are the risk factors for male breast cancer?
Aging is the primary risk factor for breast cancer in men as well as in women, says medical oncologist Ayca Gucalp, who is leading the research efforts in male breast cancer at Memorial Sloan Kettering. However, men tend to develop the disease in their late 60s or 70s, which on average is five to ten years later than women.
Increased amounts of the hormone estrogen — above the low level that is normal for men — as well as decreased levels of testosterone can also result in a higher risk for male breast cancer. These altered hormone levels may be the result of chromosomal disorders such as Klinefelter syndrome; certain conditions that affect the testicles; liver dysfunction; or medications that affect the balance of hormones, including some drugs used to treat prostate cancer.
As with breast cancer in women, a family history of the disease and mutations in the inherited genes BRCA1 and especially BRCA2 are also linked to higher incidence of breast cancer in men. These genes are linked to other cancers in men as well, such as prostate cancer and pancreatic cancer. For this reason, MSK experts, such as clinical geneticist Mark Robson, recommend that men diagnosed with breast cancer consider undergoing BRCA testing.Back to top
What are the symptoms of male breast cancer?
Most men with breast cancer are diagnosed after finding a lump or mass. “It’s very important for men to know that any mass in the breast area should not be ignored,” Dr. Gucalp says.
“Because male breast cancer is so rare, this symptom doesn’t always set off an alarm for a man to see his doctor,” she adds. “A lump doesn’t mean it’s breast cancer — more often it’s an infection or the mass is benign. But a breast mass in a male patient should always be evaluated by a physician.”Back to top
How is male breast cancer diagnosed?
Breast cancer in men tends to be diagnosed at a more-advanced stage than it is in women, because many men discount symptoms for a long time, Dr. Gucalp says. “Even after men recognize a lump and go to see a doctor, it may take longer for tests to be run because of a lack of awareness in the medical community,” she notes.
The tests used for breast cancer diagnosis are the same in men and women: a mammogram with or without an ultrasound, followed by a biopsy, in which a small sample of the tumor is removed.
“The biopsy is important to confirm a diagnosis of breast cancer and to assess the tumor’s receptor status,” Dr. Gucalp says. Studies have shown that more than 90% of male breast cancer is estrogen receptor–positive — meaning that the cancer may receive signals from estrogen that could promote tumor growth. This is a higher rate than what is seen in women; researchers aren’t sure why that is the case.Back to top
What else do we know about how breast cancer differs in men and women on a molecular level?
Another molecular test used to guide breast cancer treatment decisions is a test for the HER2 protein. Twenty percent of female breast cancers have an increased number of copies of HER2, and HER2-positive status indicates that patients are likely to respond to one of several drugs that target the HER2 protein.
However, “less is known about HER2 status in relation to male breast cancer,” Dr. Gucalp says. “The available data are varied. A few studies suggest that HER2 is less common in male breast cancer, but more research is needed.”
This summer, MSK experimental pathologist Jorge Reis-Filho published a study in which his team sequenced the tumors of 59 male breast cancer patients. They found that in addition to a lower incidence of HER2-positive status, the two most frequent alterations in female disease — in the genes PIK3CA and TP53 — are less frequent in men. He also found that men with breast cancer were more likely to have mutations in genes that affect DNA repair — including BRCA2.
“The most important message is that we should not extrapolate the results of studies we do in female breast cancer to male breast cancer,” Dr. Reis-Filho says. “When it comes to specific genetic alterations, there are important differences.”Back to top
How is male breast cancer treated?
The most common treatment for male breast cancer is mastectomy — surgical removal of all breast tissue. Depending on the stage of the disease, patients may also be given radiation treatment or chemotherapy.
But Dr. Gucalp says that although more than 90% of male breast cancers are estrogen receptor–positive, studies have found that only about 77% of men are given tamoxifen, a drug that’s used to target the estrogen receptor. “We think that more men should probably be receiving tamoxifen, but there are side effects associated with it, including hot flashes and sexual dysfunction, and these side effects have not been well studied in male patients,” she notes. “We need to look more closely at quality of life in male breast cancer patients during and after treatment.”
She adds that because male breast cancer patients tend to be older than female breast cancer patients, they are more likely to have other health problems that may lessen their ability to tolerate treatment.Back to top
What research is being conducted on male breast cancer?
MSK is one of the leading centers in a new international effort to study male breast cancer. The first part of this project was focused on retrospective analyses of past patients in order to learn more about the biology of their disease.
Current male breast cancer patients may enroll in a clinical research trial at MSK that will enable investigators to study the disease in more depth. This trial includes an expanded molecular analysis of tumors as well as a greater focus on how different treatments affect quality of life and other health conditions.
Based on the findings from these efforts, Dr. Gucalp and her colleagues plan to eventually develop clinical trials designed specifically for men with breast cancer, as well as to expand current breast cancer trials to include more male patients. MSK already has one drug trial under way that is enrolling a small number of men.
“Because there is limited published data about treating male breast cancer, we base most of our treatment recommendations on what we have learned from female breast cancer patients,” Dr. Gucalp says. “What we are learning now from clinical trials could eventually change the landscape for men with breast cancer.”