To this day, breast cancer remains to be the most common cancer for all women, and the 2nd most common cancer worldwide. According to the Breast Cancer Research Foundation, breast cancer equates to 1 in 4 of all cancers in women. Since 2008, the incidence of breast cancer has increased more than 20% globally, with the mortality rate increasing to as high as 14%, based on the World Cancer Research Fund International. To better understand breast cancer, you need to understand how any cancer can develop and how many types of breast cancer and what are their characteristics.

The first step in solving any problem is to first identify and recognize the problem. We at BA101 believe that it is our responsibility to help address this problem, by helping provide the necessary information about breast cancer. We will be posting a series of articles about breast cancer, starting with this one, the definition and types of breast cancer.

What is breast cancer?

Breast cancer occurs when cells in the breast grow abnormally, due to a genetic abnormality. According to breastcancer.org, 85-90% of breast cancer cases happen because of genetic abnormality due to the natural aging process and the physical toll the body takes, but sometimes (5%-10% of the time) because of the genetic abnormality inherited from the parents.

Cancer occurs when genes that are responsible for regulating and maintaining the healthy growth of cells malfunction, causing a mutation of the cells that lead to abnormal cell growth, which then leads to the formation of tumors. In the case of breast cancer, cancer cells develop in the breast area, either in the cells of the lobules, the glands responsible for milk production, or ducts, where milk travels from the lobules and exits the nipples. Breast cancer can also develop, although uncommon, in the fatty and fibrous connective tissues of the breasts, also known as the stromal tissues.

If left untreated, not only will cancer cells affect the surrounding breast tissue, it may also spread to the rest of the body by way of the underarm lymph nodes. Lymph nodes are small organs responsible for the filtration of foreign substances in the body. Stages of breast cancer depending on the growth of the cancer and how far it has spread.

You can learn about the different types of breast cancer, including non-invasive, invasive, and more.

Types of breast cancer

Listed below are the different types of breast cancer, based on the list published on breastcancer.org:

Ductal Carcinoma In Situ (DCIS)

• This type of breast cancer is non-invasive because it hasn’t spread beyond the milk duct into any normal surrounding breast tissue, thus the phrase “in situ” or Latin for “in place.”
• The cancer begins in the milk ducts, hence the word “ductal,” while “carcinoma” refers to the fact that the cancer begins in the skin tissue covering or lining the internal organs.
• This type of cancer may not be life-threatening, however it does increase the risk of developing invasive breast cancer.

Invasive Ductal Carcinoma (IDC) or Infiltrating Ductal Carcinoma

• This type of breast cancer is considered to be the most common type, making up 80% of all cases.
• This type of breast cancer starts in the milk ducts and spreads to the surrounding breast tissue, hence the word “invasive.”
• This type of breast cancer can spread or metastasize to the lymph nodes and other parts of the body through the lymph system and bloodstream.
• These types of cancer become more common as women age.

Invasive Ductal Carcinoma (IDC) Subtypes:

• Tubular Carcinoma of the Breast

• Small in size (1cm or less) and made up of tube-shaped structures called tubules.
• These are low-grade tumors, meaning that the cells look similar to normal, healthy cells.
• Though this type of cancer is considered invasive, it is less aggressive and grows slower compared to other invasive cancers.
• This type of cancer responds well to treatment and can be better detected through screening mammography.
• Unlikely to spread beyond the breasts.

• Medullary Carcinoma of the Breast

• The size and shape of the cancer resembles the part of the brain called the “Medulla,” hence the name “medullary.”
• Medullary carcinoma may appear high-grade because of the size and shape, however, this type of cancer is considered to be low-grade, as it grows slowly and typically does not spread to the lymph nodes. It is much easier to treat this type of cancer than other types of invasive cancer.

• Mucinous Carcinoma of the Breast

• May also be referred to as “Colloid Carcinoma”.
• Mucinous carcinoma is a rare type of breast cancer that is made up of abnormal cells that seemingly “float” in pools of “mucin,” the slimy, slippery substance that is present in mucus.
• is Mucin becomes part of the tumor and surrounds the breast cancer cells.
• According to research, only 2-3% of invasive breast cancers can be considered to be “pure” mucinous carcinomas — meaning that this is the only type of cancer present within the tumor. Invasive breast cancers, that appear to have a mucinous component within them, along with other types of cancer cells present are about 5%.
• Commonly found in women after they hit menopause, or during their 60’s to early 70’s.
• This type of cancer is less aggressive and responds well to treatment.

• Papillary Carcinoma of the Breast

• This type of breast cancer is rare, and is normally found in women after menopause.
• The characteristics of invasive papillary carcinoma include a well-defined border, with small finger-like projections.
• Moderate-grade cancer.
• In most cases, the presence of invasive papillary carcinoma is also accompanied by DCIS.

• Cribriform Carcinoma of the Breast

• This type of cancer invades the stroma (connective tissue of the breast) in nest-like formations, between the ducts and lobules.
• Another characteristic of cribriform carcinoma is that it has a distinctive holes within the tumor, making it look like swiss-cheese.
• Considered to be a low-grade type cancer.

Invasive Lobular Carcinoma (ILC)

• Also known as “Infiltrating Lobular Carcinoma.”
• This refers to cancer that has infiltrated the wall of the lobule and begun to invade the surrounding breast tissue.
• This is the second most common type of breast cancer, right next to IDC.
• This can spread to the lymph nodes and other parts of the body.
• This type of breast cancer is common to women during their 50’s and 60’s.

Inflammatory Breast Cancer (IBC)

• Rare, but aggressive type of breast cancer.
• Instead of a distinctive lump, this type of breast cancer is characterized by reddening and swelling of the breasts.
• This type of breast cancer quickly grows, and may become worse between hours and days, that is why it is advised to seek medical care as soon as symptoms appear.
• Inflammatory Breast Cancer can also affect men.

Lobular Carcinoma In Situ (LCIS)

• This type of cancer is non-invasive, thus the phrase “in situ” or Latin for “in place.” This means that the abnormal growth remains inside the lobule and does not spread to surrounding tissues.
• Characterized by abnormal cell growth in the lobules. Individuals who are diagnosed with LCIS have the tendency to have multiple lobules affected.
• Some doctors prefer the term “lobular neoplasia (a collection of abnormal cells)” because LCIS is not “true cancer,” but indicates the significant higher risk of developing breast cancer.
• Mostly found in women ages 40 – 50 years old and is extremely uncommon in men.
• LCIS does not indicate any signs or symptoms and typically does no longer show up on a mammogram. It tends to be recognized as a result of a biopsy performed on the breast for different prior reasons.

Paget’s Disease of the Nipple

• A rare type of breast cancer that collect in or around the nipple.
• This type of breast cancer normally starts in the ducts of the nipple (the passage-way of milk), then spreads to the nipple surface and areola, making it red, scaly and itchy.
• It is important to seek immediate medical attention if symptoms occur, as 97% of the time Paget’s disease of the nipple is an indicator of the presence of breast cancer, namely DCIS or invasive cancer.
• Doctors have yet to completely identify how Paget’s disease develops. One possibility is that the cancer cells begin developing within the milk ducts inside the breast and then make their way out to the nipple surface. This gives us an idea of why so many individuals with Paget’s disease of the nipple have another area of cancer within the breast. One of the other theories, is that the cells that compose the nipple itself become cancerous. This theory gives meaning to why a small number of individuals who: (1) only have Paget’s disease located in the nipple, or (2) have another type of breast cancer that appears to be entirely separate from Paget’s disease.
• Paget’s disease of the nipple is more common in women, but like other forms of breast cancer, it can also affect men.

Phyllodes Tumors of the Breast

• Meaning leaflike in greek, phyllodes refers to the shape and structure of the tumor.
• Other names for these tumors are phyllodes tumor and cystosarcoma phyllodes.
• Though the tumor grows quickly, it rarely spreads outside of the breast.
• Though aggressive in growth, Phyllodes Tumors are mostly benign. However, in some cases, the tumor is in between malignant (cancerous) or borderline malignant.
• This type of tumor may occur at any age, but is more present in women during their 40s.

Male Breast Cancer

• Though significantly rare, with a lifetime risk of 1 in 833, men have breast tissue is still a reality.
• Though male breast tissue is not as developed as females, breast cancer may still occur.

Molecular Subtypes of Breast Cancer

• Luminal A Breast Cancer

• This type of cancer is considered low-grade, grows slower compared to other types of cancer, and responds well to treatment. Luminal A breast cancer is HER2 negative, hormone-receptor (estrogen-receptor and/or progesterone-receptor positive) positive, and low levels of the protein Ki-67, a nuclear protein responsible for the speed of cancer cell growth.

• Luminal B Breast Cancer

• Like luminal A, Luminal B is also hormone receptor-positive, however, unlike the previous cancer type, Luminal B can be either HER2 positive or HER2 negative, and has a high level of Ki-67. In comparison to Luminal A, the growth of Luminal B is slightly faster, and does not respond as well to treatment.

• Triple-negative/basal-like

• This type of breast cancer is both hormone-receptor and HER2 negative and is observed to be commonly present among women with BRCA1 gene mutations.

• HER2-enriched

• Although HER2-enriched cancers are faster in growth as compared to luminal cancers and reacts poorly to treatment, they are often successfully treated through targeted therapies that are specific to the HER2 proteins like Herceptin (chemical name: trastuzumab), Perjeta (chemical name: pertuzumab), Tykerb (chemical name: lapatinib), Nerlynx (chemical name: neratinib), and Kadcyla (chemical name: T-DM1 or ado-trastuzumab emtansine).

• Normal-like

• Like luminal A, Normal-like breast cancer is hormone-receptor-positive, HER2 negative, has low levels of the protein Ki-67, however, while normal-like breast cancer responds well to treatment, it does not respond as well to treatment as compared to luminal A.

Metastatic Breast Cancer

• Also known as stage 4 breast cancer, or when the breast cancer has spread to other body parts, mainly the liver, brain, bones, and lungs.
• Cancer cells can break apart from the original tumor, and spread throughout the body by way of the bloodstream or the lymphatic system.
• According to research, 30% of women who’ve previously had early-stage breast cancer will develop metastatic breast cancer. It is also a possibility for breast cancer to return, or show up in a different part of the body even after months and years after treatment.
• The difference between metastatic tumor from other types of cancer, is that despite the differences in location, the tumor is still made up of breast cancer cells. This means that if there is a metastatic tumor in the bone, it would be made up of breast cancer cells, instead of bone cells.

Because breast cancer is an incredibly broad topic, we will be posting several articles regarding different aspects of breast cancer. Stay posted on our website to know more about breast cancer.