Understanding Breast Cancer Types & Subtypes

24 Feb 2023

Breast cancer is a disease that affects millions of women worldwide, yet it is often oversimplified and misunderstood. Many assume that all breast cancer diagnoses fall under the same umbrella and can be easily treated with surgery or chemotherapy. The reality is much more complex. Breast cancer is a group of diseases that can vary significantly in terms of their characteristics and how they are treated. In this blog, we will explore the different types and subtypes of breast cancer, highlighting the complexity of the disease and the importance of individualised treatment plans.

Non-invasive (carcinoma in-situ) vs Invasive Breast Cancer

Breast cancers are often described as:

  • Non-invasive (carcinoma in situ): known as ‘pre-cancer’, is contained within the milk ducts or lobules and has not spread outside the breast tissue.
  • Invasive: cancer cells have spread outside of the breast tissue into surrounding tissue or other areas of the body.

Types of Non-Invasive Breast Cancer

  • Ductal carcinoma in situ (DCIS): this type starts in the milk ducts of the breast and stays contained in the breast tissue. It is usually found through mammography and often treated with surgery, including lumpectomy or mastectomy, but not chemotherapy. Though this type of breast cancer is not life-threatening, it increases the risk of becoming invasive and advanced if left untreated.
  • Lobular Carcinoma in situ (LCIS): originates in the lobules (the glands that produce milk) and does not spread into surrounding breast tissue. LCIS is highly treatable if found early and rarely becomes invasive.

Types of Invasive Breast Cancer

  • Invasive ductal carcinoma (IDC): the most common type of breast cancer, accounting for about 80% of all cases. It starts in the breast's milk ducts but can spread to the surrounding tissue, lymph nodes, and other body organs if left untreated. IDC is often treated with surgery, radiation, chemotherapy, hormone therapy, or a combination.
  • Invasive lobular carcinoma (ILC): this is the second most common type of breast cancer and starts in the lobules (milk-producing glands of the breast) and may spread to other parts of the body. This type is harder to detect through physical exams and mammograms and is more likely to affect both breasts. ILC is often treated with surgery, radiation, chemotherapy, hormone therapy, or a combination.

Other types of invasive breast cancer, which are less common, include:

  • Tubular carcinoma
  • Papillary carcinoma
  • Mucinous carcinoma
  • Medullary carcinoma
  • Low-grade adenosquamous carcinoma
  • Adenocystic carcinoma

Subtypes of Breast Cancer

Subtypes are categorised by the presence of proteins, genes, or gene mutations.

  • Triple-negative breast cancer (TNBC): one of the rarest and most aggressive types and is fast-growing with a poor prognosis and an extremely high recurrence rate after initial treatment. TNBC does not have estrogen, progesterone, or HER2 receptors, meaning it does not respond to hormone therapy or drugs targeting HER2. TNBC is often treated with surgery, radiation, and chemotherapy.
  • HER2-positive breast cancer: this type has too much of a protein called HER2. This protein plays a role in making the cancer grow faster or become more aggressive. This type of breast cancer may be treated with surgery, radiation, chemotherapy, and drugs that target HER2.
  • Hormone receptor positive breast cancer (HR+): this subtype is driven by hormones like estrogen and progesterone and is treated with hormonal therapy. Two subtypes of HR+ breast cancer are estrogen positive (ER+), which contains estrogen receptors on the cancer cell, and progesterone positive (PR+), which has progesterone receptors. If a biopsy shows positive results for either receptor, it will be classed as HR+ and will usually respond better to treatment. However, treatment results and prognosis will depend on how many receptors there are on the cancer cells.

Rare, Invasive Types of Breast Cancer

  • Inflammatory breast cancer (IBC): this type accounts for only 1-5% of all cases and is caused by cancer cells blocking lymphatic vessels in the breast. It typically causes the breast to become red, swollen, and warm to the touch. IBC is often treated with a combination of chemotherapy, surgery, and radiation.
  • Paget's disease of the nipple: This type starts in the breast's milk ducts and spreads to the skin of the nipple and areola. It can cause itching, redness, and crusting of the nipple, similar to symptoms of other irritating skin conditions. Paget's disease of the nipple is often treated with surgery, radiation, and sometimes chemotherapy.
  • Phyllodes Tumours of the breast: develop in the breast's connective tissue. Phyllodes tumours can be benign (not cancerous), borderline (have the potential to become cancerous), or malignant (cancerous) and may be treated with surgery and radiation. These tumours are less likely to respond to standard breast cancer treatments like chemotherapy or hormonal therapy.
  • Male breast cancer: although breast cancer is more common in women, men can also develop breast cancer. Male breast cancer is rare, with 1 in 668 men diagnosed by age 85. It may be treated with surgery, radiation, chemotherapy, hormone therapy, or a combination.
  • Locally advanced breast cancer: also referred to as Stage 3, this type involves a large (5cm +) tumour in the breast or cancer cells that have spread beyond the breast into nearby lymph nodes but not to other parts of the body. Treatment for locally advanced breast cancer requires a combination of chemotherapy, surgery, and radiation.
  • Metastatic breast cancer (MBC): this type usually occurs when a woman has previously been diagnosed with another form of breast cancer and spreads to other parts of the body, such as the bones, lungs, brain or liver. This type may also be called stage IV or advanced breast cancer. Metastatic breast cancer is often treated with surgery, radiation, chemotherapy, hormone therapy, and targeted therapy.

Breast cancer is more than just a single disease; it’s a collection of different types of cancers with unique characteristics and treatment options that should involve personalised patient plans. Understanding the different types of breast cancer and highlighting that a diagnosis requires more than just a one-size-fits-all approach to treatment and care helps improve treatment outcomes and quality of life. It empowers patients to make more informed decisions and have confident conversations with their healthcare team.

Head to Pink Hope’s resource page, Understanding Breast Cancer, to learn more.

This content is brought to you in partnership with Eli Lilly Australia and developed independently by the team at Pink Hope in consultation with medical experts