Breast cancer is the most common type of cancer among women in the United States, accounting for more than a quarter of all cancers in women. Approximately 2.5 million women in this country are breast cancer survivors, and an estimated 192,370 new cases of breast cancer were diagnosed in women in 2009. Advances in treatment have enabled more women to live longer overall and to live longer without disease progression.

Classification of Breast Cancer

As with all cancers, the development of breast cancer starts from just one genetically abnormal cell. This abnormal cell divides and multiplies rapidly to become a mass of cells, or a tumor. As the tumor grows, it develops a blood supply to help sustain its growth. Approximately 90-95% of all breast cancers are sporadic, which means that they occur by chance. The remaining 5-10% of breast cancers are caused by inherited abnormalities in genes, known as genetic mutations. The primary breast cancer-related genetic mutations are
abnormalities in BRCA1 and BRCA2.

Breast cancer is classified by histology; that is, by the appearance of the tumor under the microscope. Most breast cancers begin in the milk ducts; breast cancer that does not spread beyond the ducts is defined as ductal carcinoma in situ (DCIS). Breast cancer that arises and remains confined to the lobules, or milk-secreting glands, is defined as lobular carcinoma in situ (LCIS). Neither DCIS nor LCIS are life-threatening because they are noninvasive; but they do increase the risk of the subsequent development of an invasive breast cancer.

Most cancers are invasive, which means that they spread beyond the tissue where they arise. Invasive ductal cancers are far more common than invasive lobular cancers, and there are several other subtypes of invasive breast tumors that are relatively rare (Table 1).

As invasive breast tumors grow, cells may break off and travel through the lymphatic system to nearby lymph nodes (tiny, bean-shaped organs that are part of the immune system); lymph nodes near the breast are located under the arm, in the neck, and just above the collarbone. Tumor cells can also travel through the bloodstream to other parts of the body; this spread of cancer is known as distant metastasis. The most common sites of distant metastasis in breast cancer are the bones, lungs, liver, and brain.

New Ways of Defining Breast Cancer

Despite significant advances in the treatment of breast cancer, not every treatment is effective for every woman. Why? In an attempt to answer that question, researchers have studied tumors from hundreds of thousands of women with breast cancer and have found that breast tumors vary in some very important ways. An enhanced understanding of the biology of tumors is leading investigators to define tumor characteristics more precisely.

Breast tumors are still classified according to histologic type, but the identification of tumor markers and the development of technology for genetic profiling (studying several genes in a tumor simultaneously) have led to an additional classification of breast cancer—one based on molecular subtypes (Table 1). Investigators have determined that more data are needed before these subtypes can be used to plan treatment; however, each of the four subtypes is typically associated with specific tumor markers such as estrogen and progesterone receptors (ER and PR) and human epidermal growth factor receptor 2 (HER2), and the presence or absence of these tumor markers has become a major factor in selecting treatment and determining prognosis (outcome).

Diagnosis and Staging

As new ways of defining breast cancer have emerged, the diagnosis of the disease has become more complex. Imaging studies can help locate tumors more accurately and detect metastasis in other parts of the body. As noted, ER, PR, and HER2 are tumor markers that play an important role in the diagnosis because of their implications for treatment. Once all diagnostic tests have been done, breast cancer is staged, which allows doctors to better select treatment options and predict prognosis.

Treatment

Breast cancer can be treated in a variety of settings, and women are encouraged to explore their options, which include accredited breast centers, National Cancer Institute (NCI)-designated centers, and clinical trials. The increasing complexity of breast cancer and its treatment calls for a team of specialists, and multidisciplinary planning is key for selecting appropriate treatment for individual women. The treatment of breast cancer has entered the era of personalized treatment, and your health care team will encourage you to participate in treatment decision-making, to ensure that the chosen treatment is right for you.

This guide is designed to help you better understand the diagnosis and treatment of breast cancer. No single guide could provide all the information you need to answer your questions about breast cancer and to make fully informed decisions. Still, you may be overwhelmed at the amount of information provided here. Read the guide slowly, and keep notes about things you don’t understand. Your health care team is a rich source of information about treatment options and side effects, and they can help you better understand what you’ve read here. You can also find more details on the Web sites listed at the end of each article.

Learn all you can about your cancer and your treatment options. Knowledge is power.

Table 1. Types of Breast Cancers

Type of Breast Cancer	Prevalence	CharacteristicsNoninvasive
Noninvasive
Ductal carcinoma in situ (DCIS)	80%	Remains confined to the ducts
Lobular carcinoma in situ (LCIS)	20%	Remains confined to the lobules
Invasive (Infiltrating)
Ductal	50-80%	Arises from the ducts and spreads beyond
Lobular	5-10%	Arises from the lobules and spreads beyond
Medullary	3-5%	Soft, fleshy tumor, often associated with BRCA1 mutations
Mucinous (colloid)	2-3%	Mucus is primary component of tumor, less likely to spread
Papillary	1-2%	Tumor has small, finger-like projections, usually occurs with DCIS
Tubular	1-2%	Small tumor, less likely to spread beyond breast
Cribriform	5-6%	Cancer cells invade connective tissue and cancer cells have "holes"
Inflammatory*	1-5%	Redness and swelling of the breast, often without a distinct lump
Molecular Subtypes*
Luminal A	42-59%	Usually ER+/PR+, HER2-, low proliferation rate (percentage of cancer cells actively dividing)
Luminal B	6-19%	Usually ER+/PR+, HER2+, high proliferation rate
Triple-negative/ basal-like	13-28%	Usually ER-/PR-, HER2-; most are associated with BRCA1-mutations, usually aggressive, with a high risk of recurrence
HER2+	7-12%

* Prevalence reflects the prevalence among all breast cancer cases.

ER = estrogen receptor, PR= progesterone receptor, HER2 = human epidermal growth factor receptor 2.

Top Ten Things You Should Know About Breast Cancer

No two breast cancers are exactly alike.

As a result, the “best” treatment plan for each woman differs. The personalized approach to breast cancer treatment involves making decisions on the basis of many factors, including the type of cancer, the stage of disease, the results of biomarker testing, the genetic make-up of the tumor and a woman’s individual preferences.
Breast cancer can be treated in a variety of settings.

Cancer treatment centers may be freestanding facilities or they may be affiliated with a community hospital or an academic teaching hospital. Some cancer centers have been recognized by the National Cancer Institute (NCI) for their scientific excellence and extensive cancer-related resources. These centers are described as “NCI-designated cancer centers.” Centers accredited by the National Accreditation Program for Breast Centers (NAPBC) also offer benefits for women with breast cancer. (See list of centers.)
It is acceptable to seek a second opinion.

Getting a second opinion from another pathologist with extensive expertise in examining breast cancers can be of benefit, especially if there was difficulty or controversy in interpreting the initial findings. Getting a second opinion about the recommended treatment plan can also be of benefit. Many health insurance policies will cover a second opinion if you or your doctor requests it. The delay of getting a second opinion usually does not affect the outcome of treatment, but be sure to ask your doctor about this.
Clinical trials offer benefits to many women with breast cancer.

People who have participated in a clinical trial have identified several advantages, including having access to the best available care, playing an active role in their own health care, and making a valuable contribution to cancer research. Some risks may also be involved. Talk to your doctor or another member of your treatment team to learn more about clinical trials for which you may be eligible. (Learn more about clinical trials.)
A team of health care professionals will be involved in your care.

Because most women with breast cancer receive more than one type of treatment, care is planned and given by a team of health care specialists rather than just one physician. The treatment team usually involves a breast surgeon or surgical oncologist, radiation oncologist, medical oncologist, breast radiologist, pathologist, and a breast reconstructive surgeon. Additional health care professionals, such as nurses, physician assistants, nutritionists, social workers and others may also collaborate to provide optimal care.
You should be an active participant in decision-making.

Learn as much as you can about your particular type of cancer so that you can be fully informed and prepared to participate in the decision-making about treatment. Your doctors will discuss options, and family and friends may offer advice. But the “right” treatment decision is the one that’s best for you, based on your own perceptions of quality of life. Consider asking each of the doctors on your team about the benefits and side effects of their portion of therapy.
Side effects of treatment can be alleviated.

Treatments for breast cancer may cause side effects, but there are now many ways to manage them. Talk to your doctor about the potential side effects of the treatment or treatments you’ve chosen and ask if there are ways to prevent or reduce these side effects. Be sure to tell your doctor or other members of your treatment team about symptoms you have so they can be managed promptly.
Help is available for financial and practical issues.

A variety of resources are available to help with expenses related to prescriptions, travel and health care equipment. Advocacy groups and community-based organizations often offer help with child care, provide transportation and even supply wigs. Ask social workers in your cancer center for information on local resources and be sure to review our list of resources for financial assistance.
Support groups offer comfort and strength.

Support groups provide an opportunity to talk with people who are facing some of the same challenges or have undergone similar treatments. Sharing your experience with others and hearing about their experiences can help reduce feelings of isolation. Many support groups are available online if you’d rather interact with others that way. Be sure to review our list of support groups.
You can take control.

A diagnosis of breast cancer is overwhelming, and it is easy to feel as if your life is out of control. But you have the power to overcome the challenges of breast cancer. Don’t be afraid to tell your doctors about your treatment preferences. Take good care of yourself by getting proper nutrition, exercise and sleep. Do whatever it takes to help you heal and feel physically and emotionally healthy, whether it be meditation, yoga, relaxation techniques, spirituality or counseling. Spend time with family and friends and be specific about what you need — and don’t need — from them. Enjoy your favorite activities. Live every day to its fullest.