Types of Breast Cancer

by Komal Narwani last updated -

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The number of women getting diagnosed with various types of breast cancer is rising at an alarming rate. 1 in 8 women in the United States is likely to develop breast cancer over the course of her lifetime. The numbers emphasize the importance of raising Breast Cancer Awareness across the globe. Every year, October is celebrated as the pink month or the breast cancer awareness month, a campaign initiated by the American Cancer Society in partnership with the pharmaceutical division of Imperial Chemical Industries.

Breast cancer originates due to the proliferation of cancerous breast cells. These cells can form a lump and remain confined to the area of origin. This kind of cancer is called a benign or non-invasive tumor. They may sometimes end up traveling to different parts of the body through the bloodstream, in that case, it is called a malignant or invasive tumor. Undoubtedly, malignant tumors are more dangerous than benign tumors as they are difficult to trace and control. Let’s have a look at the types of breast cancer in detail.

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Types of Breast Cancer

The major types of breast cancer are classified based on different factors like its origin, appearance, grade, stage, receptor status, genetic makeup, and others.

Based on the origin

This classification is based on where the cancer cells start proliferating or its histology.

  • Milk ducts: Ductal carcinoma is formed in the ducts of the breast, which carry milk from lobules (where milk is formed) to the nipples. This is the most common type of breast cancer. It has two forms: non-invasive which is called Ductal Carcinoma In Situ (DCIS) and invasive which is called Invasive Ductal Carcinoma (IDC). The IDC type is further divided into subtypes depending on its appearance.
  • Milk-producing lobules: Lobular carcinoma is formed in the breast lobules, which produce the milk. Its invasive form is called Invasive Lobular Carcinoma (ILC) or infiltrating lobular carcinoma. This is the second most common type of breast cancer.
  • Connective tissues: Sarcoma is formed in the connective tissue that is made up of muscles, blood vessels, and fat. Examples of sarcoma in the breast are phyllodes tumor and angiosarcoma. This is a rare type of breast cancer.

Sometimes, a different approach is taken instead of histology, in such cases, the physical exam findings are considered. An example of this approach is inflammatory breast cancer, a rare aggressive form of breast cancer, according to the Breast Cancer Organization. This is a form of ductal carcinoma but is distinguished from the others on the basis of its inflamed appearance.

Based on the appearance

This classification is based on how they appear under the microscope. These are usually the subtypes of Invasive Ductal Carcinoma (IDC).

  • Tubular: These cells are tiny tube-like structures called tubules.
  • Medullary: The tumor cells are soft fleshy mass and are in the form of the medulla, a part of the brain.
  • Mucinous: These tumor cells are abnormal and float in pools of mucin (the slimy ingredient of mucus).
  • Papillary: These cells have well-defined borders and have finger-like projections.
  • Cribriform: These carcinoma cells have distinct holes in them, making them appear like Swiss cheese.

Based on the grade

This classification is based on how different are they from the normal cells in the body. The lower the grade, the slower it progresses, and better the prognosis, making breast cancer awareness highly important.

  • Grade 1 tumor: These cells are well-differentiated from the normal cells and can be cured.
  • Grade 2 tumor: The cells of this grade can be moderately differentiated and there are chances of medium prognosis.
  • Grade 3 tumor: These cells are poorly differentiated and are difficult to treat.

breast cancer awareness

Based on the stage

This classification is based on how far have the cancer cells traveled in the body through the bloodstream. The grades are measured only in malignant tumors as the benign tumors are confined to lumps in particular areas. The American Joint Committee on Cancer (AJCC) and the International Union Against Cancer (UICC) jointly recommend TNM staging system, where T is for tumor, N is for nodes, M is for metastasis.

  • Stage 0: This is the pre-cancer stage also known as in situ or the marker condition. The tumor is formed in this stage.
  • Stage 1 to 3: During this stage, the cancer cells usually spread to the breasts and regional lymph nodes.
  • Stage 4: This is the last stage of breast cancer. It is also known as metastatic breast cancer. During this stage, the cancer cells spread to distant sites beyond the regional lymph nodes. There is no known cure for this stage.

Based on the receptor status

Breast cancer cells have receptors on the cell surface, in their cytoplasm and nucleus. Thus, they are able to absorb this specific protein or hormones that circulate in the body. They are classified on the basis of their receptor status. The three most important receptors are Estrogen Receptor (ER), Progesterone receptor (PR), and Human Epidermal Growth Factor Receptor 2 (HER2/neu).

  • Positive receptors: Cells having either of these receptors are called ER-positive (ER+), PR-positive (PR+), HER2-positive (HER2+).
  • Negative receptors: Cells without these receptors are called ER-negative (ER-), PR-negative (PR-), HER2-negative (HER2-).
  • All receptors: A cell having all of these receptors is called triple positive.
  • No receptors: A cell having neither of these receptors is called triple negative.

The new approach considers receptor status and grades together, classifying breast cancer into molecular subtypes. The five intrinsic molecular subtypes of breast cancer are:

  • Luminal A: This is ER+ or PR+, HER2-, and low grade.
  • Luminal B: This is ER+ or PR+, HER2+ or HER2-, and high grade.
  • HER2 enriched or HER2+: This is ER- or PR- and is amplified HER2+.
  • Basal-like: The triple negative type is also known as basal-like.
  • Claudin-low: This is triple negative but has low expression of the cell-cell junction of proteins (including claudin).

Based on the genetic makeup

A sample of tumor tissue from a biopsy, tested in a laboratory, may reveal the DNA makeup of breast cancer cells. They are differentiated based on the expression of hundreds of genes. The classification is yet underway but researchers are trying to find tumor markers in the gene which will help them diagnose the situation and provide treatment. Example, the HER2 gene marker cells have multiple copies of the HER2 gene, which produce the growth-promoting hormone.

Take away: With the growing rate of the spread of this disease, it has become highly important to educate and spread breast cancer awareness among people. A lot of research and technological advancement has made way to a lot of achievement in the diagnosis and treatment of this subject. In a recent blog post, Google has claimed that the Google AI – LYNA (Lymph Node Assitant) can tell the difference between cancer and non-cancer on slides with about 99% accuracy. However, there is still a long way to go in terms of fighting and conquering the breast cancer battle. Until then it is important to keep spreading the awareness and tell them to ‘Fight like a Girl.’

About the Author

An alumnus of St. Xavier’s College, Mumbai, Komal is a quirky writer. She loves to add a touch of creativity to everything she does. She has a diverse background in teaching biology, working as an analyst, and freelancing as a content writer. There are only two ways she can express herself, first is words and second is dance.

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