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According to the National Cancer Institute, about 1 in 8 American women will be diagnosed with breast cancer sometime in her life. It’s much less common in men with only about 1 in 800 men likely to develop it during their lifetime.

Your breast is made up of lobules and ducts surrounded by fatty and connective tissue. The glandular lobules produce milk which is transported to the nipple through the ducts.

Breast cancer occurs when normal cells in the lobules, ducts, or other breast tissue become damaged and grow out of control. The abnormal cells rapidly grow and accumulate, forming a mass called a tumor.

If a tumor grows but doesn’t spread into nearby breast tissue, it’s called benign and is not considered cancer. A malignant tumor spreads, invading surrounding tissue and is considered cancerous.

Because it can start in lobules, ducts, or other tissue, there are many different types of breast cancer.

Breast cancer can be categorized in several ways. Most often it’s classified by where it originates and whether it moves from that spot.

An easily identifiable characteristic of breast cancer is the type of cell it’s formed in.

  • Ductal carcinoma is formed in the cells lining the milk ducts.
  • Lobular carcinoma is formed in the milk-producing lobules.
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Another important characteristic of breast cancer is whether it invades surrounding tissue or stays where it originally formed.

  • Noninvasive (in situ) breast cancer has not spread into surrounding tissue.
  • Invasive (infiltrating) breast cancer has moved into the tissue surrounding it.
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Combining these classifications gives a descriptive name to the type of breast cancer as outlined below.

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The symptoms of breast cancer can vary widely and some types of breast cancer may not have any noticeable symptoms.

Sometimes a lump may be too small to be felt or to cause any changes to your breast or surrounding area. In these cases, cancerous cells are often first detected through screening techniques like a mammogram.

When there are symptoms, they can include:

  • a lump or thickening of breast tissue that you can feel with your fingers
  • breast swelling or changes to your breast size or shape
  • changes to the skin on your breast, such as dimpling, redness, or skin irritation
  • the nipple turning inward or nipple pain
  • a lump in your underarm area
  • nipple discharge other than breast milk

It’s important to be familiar with how your breasts usually look and feel. This will help you notice any changes and to follow up with your healthcare professional promptly if anything looks or feels different.

Noninvasive breast cancer develops in the cells of a duct or lobule and remains in that location. It’s also referred to as “in situ” which means “in the original place”.

There are two types of noninvasive breast cancer:

  • ductal carcinoma in situ (DCIS)
  • lobular carcinoma in situ (LCIS)

Let’s take a closer look at each type.

Ductal carcinoma in situ

  • forms in the cells lining a milk duct
  • remains in the duct and does not spread to nearby tissues
  • is considered “precancer” or “preinvasive” because, if left untreated, it can become invasive and spread into nearby tissue
  • accounts for about 15 to 20 percent of all breast cancers
  • usually only occurs in one breast
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DCIS is often curable. It’s usually treated with a lumpectomy, followed by radiation therapy or with a mastectomy.

If the cancer is hormone receptor positive, it may be treated with tamoxifen or an aromatase inhibitor (for postmenopausal patients) for 5 years after surgery. This treatment is thought to lower the risk of DCIS recurrence or invasive cancer developing in either breast.

Lobular carcinoma in situ

  • forms in the cells lining a lobule
  • remains in the lobule and does not spread to nearby tissues
  • is usually considered a change in the breast rather than cancer
  • is thought to be a marker of increased risk of developing invasive cancer
  • tends to develop in both breasts
  • is more prevalent in premenopausal women
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Treatment for LCIS requires close follow-up with your doctor due to the high risk of developing invasive breast cancer. Your LCIS may need no treatment, or your doctor may recommend it be removed with breast-conserving surgery like an excisional biopsy.

Invasive breast cancer also develops in the cells of a duct or lobule, but it doesn’t remain where it originated. Instead, it spreads and invades surrounding tissue. Another name for it is “infiltrating.”

There are two types of invasive breast cancer:

  • invasive (infiltrating) ductal carcinoma (IDC)
  • invasive (infiltrating) lobular carcinoma (ILC)

Invasive ductal carcinoma

  • forms in the cells lining a milk duct
  • spreads into nearby tissue
  • is the most common type of breast cancer, accounting for about 70 to 80 percent of all breast cancers
  • is the most common type of breast cancer found in men
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Invasive lobular carcinoma

  • forms in the cells lining a lobule
  • spreads into nearby tissue
  • is the second most common type of breast cancer accounting for about 10 to 15 percent of breast cancers
  • is a slow-growing tumor so it may not respond to chemotherapy
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Breast cancer is typically further classified based on the surface proteins that are found on the cancer cells.

When breast cancer tissue is removed from your body, it’s tested for these proteins. The cancer cells are then subtyped based on the presence or absence of surface proteins. Knowing the subtype can help your doctor determine the best course of treatment for your cancer.

Let’s look at the three most common subtypes for breast cancer.

Hormone receptor positive

This subtype has estrogen and/or progesterone receptors. An “ER positive” tumor has estrogen receptors, while a “PR positive” tumor has progesterone receptors. This subtype often needs the hormones corresponding to its receptors to grow.

It’s estimated that around 70 percent of breast cancers are estrogen receptor positive, while more than two-thirds of those are also progesterone receptor positive.

Treatment with anti-estrogen or anti-progesterone hormone therapy can block tumor growth and kill the cancer cells. If there are no receptors, it’s called a “hormone receptor negative” tumor.

HER2 positive

This subtype has extra copies of the HER2 gene, so it produces too much of a growth hormone called HER2. This hormone allows the cancer to grow more quickly.

Treatment typically involves medications that can slow the production of this hormone and kill the cancer cells.

About 20 to 25 percent of breast cancers are HER2 positive.

Triple negative

Cancers that do not have ER, PR, or HER2 receptors, are called “triple negative”.

It’s more common in women who have a BRCA1 gene mutation, so your doctor my recommend you be tested for this mutation if your cancer is triple negative.

About 10 to 15 percent of invasive breast cancers are triple negative.

Less common types of breast cancer are often named by the way they look under a microscope. Here’s a closer look at several less common types.

Inflammatory breast cancer (IBC)

Inflammatory breast cancer accounts for about 1 to 5 percent of all breast cancers. It’s a fast-growing, aggressive type of breast cancer that has different symptoms to most other types of breast cancer. Because it doesn’t present as a lump, IBC is often mistaken for other conditions.

Some of the most common symptoms of IBC include:

  • a swollen, warm, red breast
  • breast skin that’s thickened or pitted
  • a breast that feels larger or heavier than normal
  • pain or tenderness in the breast or surrounding area
  • itchiness on or around the breast
  • an inverted nipple

The symptoms of IBC are caused by a blockage of the lymphatic system within the breast. These symptoms tend to develop quickly, usually within 3 to 6 months.

Paget disease of the breast

Paget disease accounts for only up to 4 percent of all breast cancer cases.

Paget disease is a rare cancer that forms in the milk ducts and spreads to the skin of the nipple and areola, the skin around the nipple. According to the National Cancer Institute, this type of breast cancer is usually accompanied by DCIS or an invasive tumor within the breast.

The symptoms of Paget disease are often mistaken at first for skin conditions, like eczema or dermatitis. However, the symptoms won’t respond to topical treatments.

The typical symptoms of Paget disease include:

  • redness, flaking or crusting around the nipple and areola
  • a tingling or itching sensation around the nipple area
  • thickened skin on or near the nipple
  • a flattened nipple
  • bloody or yellowish discharge from the nipple

Phyllodes tumors of the breast

A phyllodes tumor is a very rare type of breast cancer that accounts for less than 1 percent of all breast tumors

In about 75 percent of cases, phyllodes tumors aren’t cancerous, so they usually don’t spread beyond the breast. But they can grow quickly and some can be considered “borderline,” which means they have properties that could make them cancerous at a later stage.

Phyllodes tumors form in the connective tissue of the breast. The most common symptoms include:

  • a smooth lump in or around the breast
  • a lump that grows quickly and stretches the skin
  • breast skin that looks red and feels warm

Tubular carcinoma of the breast

Tubular carcinoma is a subtype of invasive ductal carcinoma (IDC). This type of breast cancer gets its name due to the tube-shaped structures, which can be seen under a microscope, that make up the tumor. The tumors are usually small (about 1 centimeter or less) and tend to grow slowly.

Tubular carcinoma is rare, accounting for up to 2 percent of invasive breast cancers.

Because these tumors are small, they are most often detected during a routine mammogram. They tend to be low grade with good prognosis.

Mucinous (colloid) carcinoma of the breast

Mucinous carcinoma, also known as colloid carcinoma, is a rare form of invasive ductal carcinoma (IDC). About 2 percent of breast cancers are “pure” mucinous carcinoma, while up to 7 percent of breast cancers have some component of mucinous carcinoma cells.

With this type of cancer, the tumor consists of abnormal cells that appear to “float” in pools of mucus when looked at under a microscope.

It’s typically a less aggressive type of cancer that has a lower probability of spreading to the axillary (underarm) lymph nodes than some other types of IDC.

Mucinous carcinoma tends to be more common in post-menopausal women, with the average age at diagnosis being around 60 to 70 years of age.

Medullary carcinoma of the breast

Medullary carcinoma of the breast is another rare subtype of invasive ductal carcinoma (IDC). It accounts for around less than 5 percent of all breast cancer cases.

The tumor is typically a soft, fleshy mass rather than a lump in the breast tissue. The mass most often develops in the middle of the breast and is most often found in women with the BRCA1 mutation.

Although these cancer cells often have an aggressive appearance, they don’t grow quickly and usually don’t spread to the lymph nodes. This makes it easier to treat than some other types of breast cancer.

The treatment of breast cancer varies depending on many factors, such as:

Possible treatment options for breast cancer include:

  • Lumpectomy. This breast-conserving surgery is usually used for smaller, less invasive tumors. It involves only removing the tumor and some surrounding tissue.
  • Mastectomy. With a mastectomy, the entire breast is removed. The type of mastectomy can differ depending on how invasive the cancer is.
  • Radiation therapy. Radiation therapy is often used to destroy any cancer cells remaining in the breast or surrounding tissue after surgical removal of the cancer.
  • Chemotherapy. Chemotherapy medication is often used to destroy cancer cells that have spread to distance parts of the body.
  • Hormone therapy. Anti-estrogen and anti-progesterone therapy can be used to slow the growth of hormone receptor-positive tumors.
  • Immunotherapy. Immunotherapy is a way to stimulate your immune system so that it’s able to recognize and attack cancer cells. This is a growing area of research that’s continuing to find new ways to treat cancer.
  • Other targeted therapy. For HER2-positive breast cancer, some types of targeted therapy can detect and disrupt the growth-promoting proteins on the surface of the cancer cells. This may help slow the growth of HER2-positive tumors.

Regular breast self-examinations, and mammograms help detect breast cancer in its early stages. Finding breast cancer that has not yet spread gives you the best chance of remaining healthy and cancer-free for many years.

According to the American Cancer Society, on average, when your breast cancer is treated before it has spread, you’re 99 percent as likely to be alive in 5 years as someone who does not have breast cancer.

Other steps you can take to lower your risk of getting breast cancer include the following:

  • Limit alcohol to no more than one drink a day.
  • Maintain a moderate weight throughout your life.
  • Stay physically active.
  • Breastfeed if you can.
  • Avoid hormone therapy for postmenopausal symptoms.
  • Avoid breast implants.
  • Talk to your doctor about medication or surgical treatments to reduce the chances you will get breast cancer if you are at high risk.

There are many types of breast cancer. Some types of breast cancer develop in the milk-producing lobules in your breast while others grow in the cells lining the milk ducts. Some tumors are benign and noninvasive, but others can be malignant, invading nearby breast tissue.

Breast cancer can be treated with surgery, chemotherapy, radiation therapy, targeted medication, and hormone therapy. However, you’ll need less treatment if breast cancer is detected early through breast self-examinations or routine mammograms.