Many women worry that one day, they may find a lump in their breast or that a routine mammogram will show something abnormal in the breast tissue that turns out to be cancer. That’s because breast cancer is among the most common cancers in women. A woman in the U.S. has a 1 in 8 chance of developing breast cancer over the course of her lifetime and over 3.5 million American women currently have breast cancer. In 2021 alone, an estimated 281,550 women will be newly diagnosed with the disease.

While breast cancer is a serious disease, its mortality rate has been in declining since the early 1990s. Over that same period, the 5-year survival rate has been on the rise, thanks in large part to increased use of screening mammography and improved treatments.

“The treatment of breast cancer has certainly improved over the last few decades through personalized treatment plans that are developed by multidisciplinary specialists, including those in surgery, radiation, and medical oncology based on the latest evidence in clinical trials,” says Maryam Lustberg, MD, MPH, director of The Breast Center at Smilow Cancer Hospital and chief of Breast Medical Oncology at Yale Cancer Center.

Breast cancer develops when cells in the breast grow in an abnormal and uncontrolled manner. Over time, these cells can form tumors. In most cases, these tumors are benign, meaning they are non-cancerous and do not spread to other parts of the body.

But sometimes, cancerous tumors form. The cells that make up cancerous tumors are malignant, meaning they can invade neighboring tissues and may even spread to distant parts of the body.

The breasts are made up of a combination of glandular, connective, and fatty tissues. The glandular tissues contain milk-producing glands and ducts which transporting milk from the glands to the nipple during breastfeeding. While cancer can develop in any of these breast tissues, it most commonly occurs in the lobules and ducts.

There are several types of breast cancer, including:

• Ductal carcinoma. These cancers arise from cells in the milk-carrying ducts of the breast. This is the most common form of breast cancer.
• Lobular carcinoma. This form of cancer occurs in the milk-producing lobules of the breast.
• Sarcoma. Breast sarcomas develop in the connective tissues of the breast. Sarcoma is a rare type of breast cancer. 
• Inflammatory breast cancer. This is a rare but aggressive form of breast cancer that usually begins in the milk ducts and spreads to other parts of the breast.
• Paget’s disease of the breast. This rare type of cancer affects the nipple and areola.

Ductal and lobular breast cancers are further classified based on whether they are non-invasive or invasive.

• Non-invasive breast cancer, known as “carcinoma in situ,” occurs when cancer develops in the milk ducts or lobules, but has not yet spread to other tissues in the body. There are two common types of non-invasive breast cancers, ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS).
• Invasive breast cancers, by contrast, can spread to nearby lymph nodes and other parts of the body. Invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) are two common types of invasive breast cancer.

Breast cancers are also categorized by their hormone receptors (estrogen and progesterone) and HER2 status.

Breast cancer cells that contain receptors for hormones like estrogen and/or progesterone (which can help the cancer cells grow) are said to be hormone receptor-positive, or HR-positive. And cancer cells that have high levels of receptors, known as human epidermal growth factor receptor 2 (HER2), are classified as HER2-positive. HER2 is a protein that helps HER2-positive cancer cells grow.

Cancer cells that do not contain hormone and/or HER2 receptors are called hormone receptor-negative or HER2-negative. Breast cancers that do not have receptors for estrogen, progesterone, and HER2 are known as triple-negative.

When cancer that originates in the breast spreads, or metastasizes, to other parts of the body beyond the lymph nodes, it is known as metastatic breast cancer; it is sometimes called Stage IV or advanced breast cancer.

Metastatic breast cancer can spread to just about any part of the body, but it most often spreads to the liver, lung, brain, or bones. Treatment of metastatic breast cancer aims to slow its progression, relieve symptoms, and help women live longer.

Non-modifiable factors that increase the risk for breast cancer include:

• Age. Women over age 40 are more likely to develop breast cancer and risk increases as women age
• Personal or family history of breast and ovarian cancer
• Inherited gene mutations such as BRCA1, BRCA2, PALB2, and CHEK2 among others
• Atypical hyperplasia (a condition in which abnormal cells in the breast proliferate)
• Dense breasts
• Early age of first menstruation (under age 11 or 12)
• Late menopause (over age 55)
• Radiation to chest area prior to age 30

Other risk factors that a woman may be able to control include:

• Alcohol consumption
• Physical inactivity
• Long-term hormone replacement therapy with estrogen and progestin together
• Late age of first pregnancy (over age 30) or never giving birth
• Not breastfeeding a child
• Postmenopausal obesity
• Hormonal contraceptives (marginally increases risk)

Early-stage breast may not cause any noticeable symptoms and may only be identified with a routine screening mammogram. But it can cause a range of symptoms including:

• Lump or mass in the breast, which is usually painless
• Changes in shape or size of the breast
• Changes to skin of breast (reddening, thickening, or dimpling of skin)
• Warm breast
• Swollen lymph nodes in armpit or above collarbone
• Nipple changes, including discharge, blistering, pain, and inversion
• Breast pain

Breast cancer screening aims to detect breast cancer at an early stage, before it has a chance to spread and when it is easiest to treat. Screening for breast cancer may include the following tests:

• Mammograms and other imaging tests. Mammography, which captures an image of the breast using an X-ray, is the most widely used screening test, though sometimes other imaging tests such as magnetic resonance imaging (MRI) and ultrasounds are used. Because the risk of breast cancer increases with age, the U.S. Preventive Services Task Force recommends screening mammograms every two years for women between ages 40 and 74 who are at average risk for breast cancer. Women who are at higher-than-average risk for breast cancer may be advised to begin screening at a younger age and to undergo more frequent screening tests. Women should talk to their doctor about when to begin screening and which screening tests are most appropriate for them.
  
  Screening mammography is often performed using digital breast tomosynthesis (DBT), sometimes called three-dimensional (3D) mammography or breast tomosynthesis. Conventional mammography produces a two-dimensional image of breast tissue. In DBT, the mammogram machine travels over the breast in an arc, producing multiple images taken from several angles that radiologists can view on a monitor. Studies have shown that DBT offers improved detection rates and reduces the rate of getting called back for further testing.
• Clinical breast examination (CBE). A health care provider will physically examine a woman’s breasts to check for lumps or other abnormalities that may suggest breast cancer. CBE is often reserved for women at higher-than-average risk of breast cancer.
• Breast self-awareness. Women should become familiar with how their breasts look and feel so that they can detect changes that may be related to breast cancer.

A diagnosis of breast cancer typically begins when a screening mammogram identifies an abnormality in breast tissue or when a woman feels a lump or notices other changes to her breast. It is important to know that in many cases, these findings turn out to be benign, or noncancerous. Additional testing is necessary, however, to determine if cancer is present.

The doctor will begin his or her diagnosis by asking about medical history, including whether the patient has any risk factors associated with breast cancer. The doctor will perform an exam during which he or she feels the breasts, nipples, and nearby lymph nodes to check for lumps, swelling, or other abnormalities. The doctor may order bloodwork and imaging tests such as a mammogram, ultrasound, or MRI to help make a diagnosis.

But the only test that can definitively diagnose cancer is a biopsy. In this procedure, a doctor will remove a small amount of breast tissue. This is usually done using a needle, though sometimes a surgical procedure is necessary. If a breast abnormality is found on the skin, a punch biopsy—a procedure that removes a small piece of skin using a special tool—may be used. 

A pathologist will then examine the tissue to check for the presence of cancer cells. If cancer cells are present, the pathologist will determine the type of breast cancer and its hormone receptor and HER2 status.

If breast cancer is diagnosed, the doctor will order additional tests to see if the cancer has spread to other parts of the body. This process is known as staging and it may involve a sentinel lymph node biopsy as well as other imaging tests such as a chest X-ray, computed tomography (CT), positron emission tomography (PET), or a bone scan.  Testing is individualized to the stage and type of presentation of the cancer. Once the size of the primary tumor and the extent of the spread (if any) has been established, the doctor will use this information to determine the stage of the cancer. This helps the doctor make a prognosis and formulate the best treatment plan for you.

Breast cancer treatment usually involves one or more of the following therapies:

• Surgery
• Radiation therapy
• Chemotherapy
• Hormone therapy
• Targeted therapy

Surgery. Often the first-line treatment, surgery is used to remove the cancerous tumor. In some cases, the surgeon can perform a breast-conserving procedure that preserves as much of the breast as possible. In other cases, a mastectomy is necessary. This is a procedure in which the entire breast is removed. Women who undergo breast conserving surgery or mastectomy may wish to talk to their surgeon about breast reconstruction surgery options. In recent years, certain breast cancers are first treated with preoperative chemotherapy (neoadjuvant chemotherapy) and then precede to surgery.

Radiation Therapy. Sometimes called radiotherapy, radiation therapy kills cancer cells by exposing them to radiation. Radiation therapy is usually used following surgery to eliminate any remaining cancer cells. A type of high-dose radiation therapy known as hypofractionated radiation therapy is sometimes used to treat breast cancer. It usually requires fewer treatment sessions than other types of radiation therapy.

Chemotherapy. Chemotherapy uses drugs to damage or kill cancer cells. Chemotherapy may be given before or after surgery with the purpose of reducing tumor size and eliminating residual cancer cells in the body.  

Hormone therapy. Hormone therapy is used to treat hormone receptor-positive breast cancers. Some of these medications work by reducing the body’s production of the hormones estrogen or progesterone. This deprives cancer cells of hormones that help them grow. Other medications prevent hormones from binding to receptors on cancer cells, which stops or slows the growth of cancer cells.

Targeted HER2 therapies. Several medications are used to treat HER2-positive breast cancer. These drugs target the HER2 protein and slow or stop cancer cell growth. They may be used to reduce the size of the tumor prior to surgery or following surgery to stop or slow the growth of any cancer cells that remain.

The prognosis for breast cancer depends on several factors. These include when the cancer was detected, its type and invasiveness, and the age and overall health of the patient at the time of diagnosis. But in general, breast cancers that are detected at early stages are easier to treat and have the best outcomes. The five-year survival rate for women with breast cancer that has not spread beyond the breast is 99%. For women with metastatic breast cancer, the five-year survival rate is 29%.

It’s important that even women who have been successfully treated for breast cancer should continue follow-up care with a health care provider. Regular mammograms and other screening tests are important for monitoring the possible recurrence of breast or other types of cancer.

“We believe in collaborative multidisciplinary care taking into account the latest advances in breast cancer, as well as ensuring patient-centered care,” says Dr. Lustberg. “We are committed to continuing to make progress to improve outcomes in breast cancer as a team.”