The cancer can develop in any of the three types of breast tissue: lobules, ducts, and connective tissue.

Most cancer begins in the lobules (the milk-producing glands), or in the ducts, along which milk travels to the nipple. But tumours can also develop in the fibrous and fatty connective tissue that surrounds the lobules and ducts.

Several different types of breast cancer exist. The type of breast cancer and its stage, or how far it has grown, determine the treatment for it.

Breast cancer that spreads into normal tissue is called invasive breast cancer. Non-invasive breast cancer stays within the breast lobule or duct.

Breast Cancer Is a Common Disease — but Numbers Are Going Down

Breast cancer makes up about 30 percent of new cancer diagnoses in women and 15 percent of all new cancer diagnoses each year. However, the rate of breast cancer cases began dropping in the year 2000 and have continued declining since.

About one in eight women will be diagnosed with invasive breast cancer at some point in their lives. Breast cancer can occur in anyone with breast tissue, but it’s much rarer in men than in women.

The disease is more common in middle age. About one in four breast cancer cases occur in women between ages 55 and 64. Among women younger than 45, black women have the highest risk of breast cancer. Black women are also more likely to die from breast cancer than women of other races or ethnicities. At least some of this increased risk is due to less access to follow-up care after an abnormal mammogram and lower rates of health insurance.

Rates of death from breast cancer have been decreasing since 1989. The majority of women survive this cancer. Overall, 89.7 percent of women will survive at least five years after being diagnosed with breast cancer. As of 2015, more than 3.4 million women in the US were living with breast cancer.

Finding Your Best Treatment Team

After receiving a diagnosis, you will have several decisions to make about the healthcare providers who will handle your treatment.

Cancer treatment usually involves a team of people, such as a surgeon, a medical oncologist, a nurse practitioner, a counselor, a patient navigator, and specialists associated with your cancer type.

Factors to consider in choosing your oncologist and treatment team are their expertise in your cancer type, what your insurance will cover, your ability to travel to and from appointments and procedures, and recommendations from others.

Even after you have a treatment team, it is a good idea to look for another oncologist to get a second opinion on your diagnosis and treatment options. It is acceptable and sometimes common to change doctors during your treatment if needed