When a man is diagnosed with breast cancer, a number of tests may be performed to determine the type of disease he has. This information is vital to choosing the best treatment plan for each individual patient.

There are several types of breast cancer, and sometimes more than one type is seen in the same patient. Determining the type of tumor is also important in helping to predict how likely it is that the cancer will spread to other parts of the body and which type of therapy is most appropriate if it already has.

Hormone Receptor Status

In about 90 percent of male breast cancer patients, tumors grow in response to the hormones estrogen or progesterone. In these tumors, cancer cells have receptors for estrogen (called ER positive), progesterone (PR positive), or both. Tumors such as these are likely to respond to hormonal therapies, which take advantage of the cancer cells’ dependence on hormones for growth. The drug tamoxifen, for example, acts by blocking a tumor’s estrogen receptors.

HER2/neu Status

HER2/neu is a gene that, when activated, helps tumors grow by producing a specific growth-stimulating receptor. Patients with tumors that have more than normal amounts of this protein (called HER2 positive) may benefit from the drug trastuzumab (Herceptin^®), which blocks the growth of tumors activated by the gene, or from a similar drug called pertuzumab (Perjeta^®). Men with breast cancer are less likely than women to have tumors that are HER2 positive.

Gene-Expression Profiling

Gene-expression profiling — tests that look at the molecular features of a tumor — also can help to determine the optimal treatment for each patient.

Oncotype DX^® is one test that may be used to help guide decisions on whether chemotherapy should be given after surgery. It analyzes 21 genes in patients with breast tumors that are ER positive. Test results are translated into a recurrence score, which enables doctors to predict which patients will benefit most from chemotherapy. However, this test was developed using data from women with breast cancer, and there is little information on how the results might apply to men.

In special cases, we may also look for mutations using a test developed at MSK called MSK-IMPACT™. It assesses more than 400 genes known to be associated with cancerous tumors. Please note that not all patients are eligible, and only invasive carcinoma is suitable for testing. If you do qualify and we identify a specific mutation in a breast cancer or in one of its metastases, you may be able to enroll in a clinical trial that tests the effectiveness of new therapies targeting those specific genetic alterations. The MSK-IMPACT test is available only to patients are seen in consultation or treated at MSK.