Breast cancer occurs almost entirely in women, but men can get breast cancer, too. It’s important to understand that most breast lumps are benign and not cancer (malignant). Non-cancer breast tumors are abnormal growths, but they do not spread outside of the breast. They are not life threatening, but some types of benign breast lumps can increase a woman's risk of getting breast cancer. Any breast lump or change needs to be checked by a health care professional to find out if it is benign or malignant (cancer) and if it might affect your future cancer risk.

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Ductal Carcinoma In Situ (DCIS)

DCIS is also called intraductal carcinoma or stage 0 breast cancer. DCIS is a non-invasive or pre-invasive breast cancer. This means the cells that line the ducts have changed to cancer cells but they have not spread through the walls of the ducts into the nearby breast tissue.

Because DCIS hasn’t spread into the breast tissue around it, it can’t spread (metastasize) beyond the breast to other parts of the body.
However, DCIS can sometimes become an invasive cancer. At that time, the cancer has spread out of the duct into nearby tissue, and from there, it could metastasize to other parts of the body.
Right now, there’s no good way to know for sure which will become invasive cancer and which ones won’t, so almost all women with DCIS will be treated.

Invasive Breast Cancer (IDC/ILC)

Breast cancers that have spread into surrounding breast tissue are known as invasive breast cancers.
Most breast cancers are invasive, but there are different types of invasive breast cancer. The two most common are invasive ductal carcinoma and invasive lobular carcinoma.
Inflammatory breast cancer is also a type of invasive breast cancer. 
Invasive (infiltrating) ductal carcinoma (IDC)This is the most common type of breast cancer. About 8 in 10 invasive breast cancers are invasive (or infiltrating) ductal carcinomas (IDC).
IDC starts in the cells that line a milk duct in the breast. From there, the cancer breaks through the wall of the duct, and grows into the nearby breast tissues. At this point, it may be able to spread (metastasize) to other parts of the body through the lymph system and bloodstream.
Invasive lobular carcinoma (ILC)
ILC starts in the breast glands that make milk (lobules). Like IDC, it can spread (metastasize) to other parts of the body. Invasive lobular carcinoma may be harder to detect on physical exam and imaging, like mammograms, than invasive ductal carcinoma. And compared to other kinds of invasive carcinoma, it is more likely to affect both breasts. About 1 in 5 women with ILC might have cancer in both breasts at the time they are diagnosed.
Less common types of invasive breast cancerThere are some special types of breast cancer that are sub-types of invasive carcinoma. They are less common than the breast cancers named above and each typically make up fewer than 5% of all breast cancers. These are often named after features of the cancer cells, like the ways the cells are arranged.
Some of these may have a better prognosis than the more common IDC. These include:

• Adenoid cystic (or adenocystic) carcinoma
• Low-grade adenosquamous carcinoma (this is a type of metaplastic carcinoma)
• Medullary carcinoma
• Mucinous (or colloid) carcinoma
• Papillary carcinoma
• Tubular carcinoma

Some sub-types have the same or maybe worse prognoses than IDC. These include:

• Metaplastic carcinoma (most types, including spindle cell and squamous, except low grade adenosquamous carcinoma)
• Micropapillary carcinoma
• Mixed carcinoma (has features of both invasive ductal and invasive lobular)

In general, all of these sub-types are still treated like IDC.

Triple-negative Breast Cancer

Triple-negative breast cancer (TNBC) accounts for about 10-15% of all breast cancers. The term triple-negative breast cancer refers to the fact that the cancer cells don’t have estrogen or progesterone receptors (ER or PR) and also don’t make any or too much of the protein called HER2. (The cells test "negative" on all 3 tests.) These cancers tend to be more common in women younger than age 40, who are Black, or who have a BRCA1 mutation.

TNBC differs from other types of invasive breast cancer in that it tends to grow and spread faster, has fewer treatment options, and tends to have a worse prognosis (outlook).

Triple-negative breast cancer can have the same signs and symptoms as other common types of breast cancer.

​Once a breast cancer diagnosis has been made using imaging tests and a biopsy, the cancer cells will be checked for certain proteins. If the cells do not have estrogen or progesterone receptors (ER or PR), and also do not make any or too much of the HER2 protein, the cancer is considered to be triple-negative breast cancer.

Inflammatory Breast Cancer

Inflammatory breast cancer (IBC) is rare and accounts for only 1% to 5% of all breast cancers. Although it is a type of invasive ductal carcinoma, its symptoms, outlook, and treatment are different. IBC causes symptoms of breast inflammation like swelling and redness, which is caused by cancer cells blocking lymph vessels in the skin causing the breast to look "inflamed."
Inflammatory breast cancer (IBC) differs from other types of breast cancer in many ways:

• IBC doesn't look like a typical breast cancer. It often does not cause a breast lump, and it might not show up on a mammogram. This makes it harder to diagnose.
• IBC tends to occur in younger women (younger than 40 years of age).
• Black women appear to develop IBC more often than White women.
• IBC is more common among women who are overweight or obese.
• IBC tends to be more aggressive—it grows and spreads much more quickly—than more common types of breast cancer.
• IBC is always at least at a locally advanced stage when it’s first diagnosed because the breast cancer cells have grown into the skin. (This means it is at least stage III.)
• In about 1 of 3 cases, IBC has already spread (metastasized) to distant parts of the body when it is diagnosed. This makes it harder to treat successfully.
• Women with IBC tend to have a worse prognosis (outcome) than women with other common types of breast cancer.

Inflammatory breast cancer (IBC) can cause a number of signs and symptoms, most of which develop quickly (within 3 to 6 months), including:

• Swelling (edema) of the skin of the breast
• Redness involving more than one-third of the breast
• Pitting or thickening of the skin of the breast so that it may look and feel like an orange peel
• A retracted or inverted nipple
• One breast looking larger than the other because of swelling
• One breast feeling warmer and heavier than the other
• A breast that may be tender, painful, or itchy
• Swelling of the lymph nodes under the arms or near the collarbone

If you have any of these symptoms, it does not mean that you have IBC, but you should see a doctor right away. Tenderness, redness, warmth, and itching are also common symptoms of a breast infection or inflammation, such as mastitis if you’re pregnant or breastfeeding. Because these problems are much more common than IBC, your doctor might suspect infection at first as a cause and treat you with antibiotics.
Treatment with antibiotics may be a good first step, but if your symptoms don’t get better in 7 to 10 days, more tests need to be done to look for cancer. Let your doctor know if it doesn't help, especially if the symptoms get worse or the affected area gets larger. The possibility of IBC should be considered more strongly if you have these symptoms and are not pregnant or breastfeeding, or have been through menopause. Ask to see a specialist (like a breast surgeon) if you’re concerned.
IBC grows and spreads quickly, so the cancer may have already spread to nearby lymph nodes by the time symptoms are noticed. This spread can cause swollen lymph nodes under your arm or above your collar bone. If the diagnosis is delayed, the cancer can spread to distant sites.
How is inflammatory breast cancer diagnosed?Imaging testsIf inflammatory breast cancer (IBC) is suspected, one or more of the following imaging tests may be done:

• Mammogram
• Breast ultrasound
• Breast MRI (magnetic resonance imaging) scan

Often a photo of the breast is taken to help record the amount of redness and swelling before starting treatment.

Angiosarcoma of the Breast

Angiosarcoma is a rare cancer that starts in the cells that line blood vessels or lymph vessels. Many times, it's a complication of previous radiation treatment to the breast. It can happen 8-10 years after getting radiation treatment to the breast.

Angiosarcoma can cause skin changes like purple-colored nodules and/or a lump in the breast. It can also occur in the affected arms of women with lymphedema, but this is not common. (Lymphedema is swelling that can develop after surgery or radiation therapy to treat breast cancer.) 

One or more of the following imaging tests may be done to check for breast changes:

• Diagnostic mammogram
• Breast ultrasound
• Breast MRI (magnetic resonance imaging) scan

Angiosarcoma is diagnosed by a biopsy, removing a small piece of the breast tissue and looking at it closely in the lab. Only a biopsy can tell for sure that it is cancer.

Paget Disease of the Breast

Paget disease of the breast is a rare type of breast cancer involving the skin of the nipple and the areola (the dark circle around the nipple). Paget disease usually affects only one breast. In 80-90% of cases, it’s usually found along with either ductal carcinoma in situ (DCIS) or infiltrating ductal carcinoma (invasive breast cancer).

​The skin of the nipple and areola often looks crusted, scaly, and red. There may be blood or yellow fluid coming out of the nipple. Sometimes the nipple looks flat or inverted. It also might burn or itch. Your doctor might try to treat this as eczema first, and if it does not improve, recommend a biopsy.

Most people with Paget disease of the breast also have tumors in the same breast. One or more of the following imaging tests may be done to check for other breast changes:

• Diagnostic mammogram
• Breast ultrasound
• Breast MRI (magnetic resonance imaging) scan

Paget disease of the breast is diagnosed by a biopsy, removing a small piece of the breast tissue and looking at it closely in the lab. In some cases, the entire nipple may be removed. Only a biopsy can show for sure that it is cancer.

Phyllodes Tumors of the Breast

Phyllodes tumors (or phylloides tumors) are rare breast tumors that start in the connective (stromal) tissue of the breast, not the ducts or glands (which is where most breast cancers start). Most phyllodes tumors are benign and only a small number are malignant (cancer).
Phyllodes tumors are most common in women in their 40s, but women of any age can have them. Women with Li-Fraumeni syndrome (a rare, inherited genetic condition) have an increased risk for phyllodes tumors.
Phyllodes tumors are often divided into 3 groups, based on how they look under a microscope:

• Benign (non-cancerous) tumors account for more than half of all phyllodes tumors. These tumors are the least likely to grow quickly or to spread.
• Borderline tumors have features in between benign and malignant (cancerous) tumors.
• Malignant (cancerous) tumors account for about 1 in 4 phyllodes tumors. These tend to grow the fastest and are the most likely to spread or to come back after treatment.

Phyllodes tumors are usually felt as a firm, painless breast lump, but some may hurt. They tend to grow large fairly quickly, and they often stretch the skin.
Sometimes these tumors are seen first on an imaging test (like an ultrasound or mammogram), in which case they’re often hard to tell apart from fibroadenomas. 
The diagnosis can often be made with a core needle biopsy, but sometimes the entire tumor needs to be removed (during an excisional biopsy) to know for sure that it’s a phyllodes tumor, and whether it's malignant or not.

Breast cancers can start from different parts of the breast. Each breast is made up of glands, ducts, and fatty tissue. In women, the breast makes and delivers milk to feed newborns and infants. The amount of fatty tissue in the breast determines the size of each breast.
The breast has different parts:

• Lobules are the glands that make breast milk. Cancers that start here are called lobular cancers.
• Ducts are small canals that come out from the lobules and carry the milk to the nipple. This is the most common place for breast cancer to start. Cancers that start here are called ductal cancers.
• The nipple is the opening in the skin of the breast where the ducts come together and turn into larger ducts so the milk can leave the breast. The nipple is surrounded by slightly darker thicker skin called the areola. A less common type of breast cancer called Paget disease of the breast can start in the nipple.
• The fat and connective tissue (stroma) surround the ducts and lobules and help keep them in place. A less common type of breast cancer called phyllodes tumor can start in the stroma.
• Blood vessels and lymph vessels are also found in each breast. Angiosarcoma is a less common type of breast cancer that can start in the lining of these vessels. The lymph system is described below.

A small number of cancers start in other tissues in the breast. These cancers are called sarcomas and lymphomas and are not really thought of as breast cancers.

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