Understanding Breast Cancer
Receiving a breast cancer diagnosis can involve a lot of new information, often delivered at a time when there is already a great deal to process. It is not uncommon to forget details about your diagnosis or feel unsure about what terms such as type, subtype, grade, hormone receptor status, HER2 status and stage mean.
Your diagnosis may also become clearer over time as pathology results and additional testing provide more information. Having a better understanding of these terms can help you make sense of your results and feel more informed when discussing your diagnosis and treatment with your healthcare team.
In this blog, we break down the different types and subtypes of breast cancer, pathology and staging, explaining what these terms mean and why they are important.
Understanding Non-Invasive vs. Invasive Breast Cancer
Before exploring the different types of breast cancer, it is helpful to understand the difference between non-invasive and invasive disease.
Non-Invasive Breast Cancer
Non-invasive breast cancer means abnormal cells remain confined within the milk ducts or lobules and have not spread into surrounding breast tissue. These cancers are often referred to as carcinoma in situ, meaning ‘in its original place.’
The two main forms are:
- Ductal Carcinoma In Situ (DCIS)
- Lobular Carcinoma In Situ (LCIS)
Although DCIS requires treatment, LCIS is generally considered a marker of increased future breast cancer risk rather than a true cancer that requires treatment.
Invasive Breast Cancer
Invasive breast cancer occurs when cancer cells break through the walls of the ducts or lobules and invade surrounding breast tissue. Importantly, invasive does not necessarily mean the cancer has spread throughout the body. It simply means the cancer has extended beyond where it first developed. Some invasive breast cancers remain confined to the breast, while others spread to nearby lymph nodes or distant organs.
Types of Breast Cancer
Breast cancer is classified according to where it begins and whether it has spread beyond its original location.
Ductal Carcinoma In Situ (DCIS)
Ductal Carcinoma In Situ (DCIS) is considered the earliest form of breast cancer and is often referred to as Stage 0 breast cancer. It is the most common type of in situ breast cancer, accounting for approximately 80–90% of all diagnosed non-invasive breast cancers.
In DCIS, abnormal cells develop within the milk ducts but remain confined to the duct lining without invading surrounding breast tissue. Although DCIS is not life-threatening, treatment is recommended because some cases may progress to invasive breast cancer over time. DCIS is frequently detected through BreastScreen mammography before symptoms develop, often seen as tiny calcium deposits known as microcalcifications.
Treatment depends on the size and extent of disease and may include:
- Lumpectomy (breast-conserving surgery)
- Radiation therapy following surgery
- Mastectomy for more extensive disease
- Hormone therapy for selected hormone receptor-positive cases
Lobular Carcinoma In Situ (LCIS)
Despite its name, Lobular Carcinoma In Situ (LCIS) is not considered breast cancer. It is much less common than DCIS, accounting for approximately 10–20% of non-invasive breast lesions.
LCIS occurs when abnormal cells develop inside the milk-producing lobules but remain completely contained within the lobules. Rather than behaving like cancer, LCIS is considered a marker that indicates an increased risk of developing invasive breast cancer in either breast in the future.
Most people with LCIS do not require treatment. Instead, management typically involves:
- Regular breast screening
- Ongoing surveillance
- Individualised risk assessment
- Occasionally risk-reducing medication for selected people
Invasive Ductal Carcinoma (IDC)
Invasive Ductal Carcinoma (IDC), also called Invasive Carcinoma of No Special Type (NST), is the most common type of breast cancer and accounts for approximately 70–80% of invasive breast cancers.
IDC begins within the milk ducts before breaking through the duct wall into surrounding breast tissue. Once invasive, it has the potential to spread through lymphatic vessels or the bloodstream to nearby lymph nodes or other organs. IDC varies considerably in behaviour. Some tumours are slow growing and low grade, while others grow more rapidly.
Symptoms may include:
- A breast lump
- Breast thickening
- Skin dimpling
- Nipple inversion
- Nipple discharge
- Enlarged lymph nodes in the armpit
Treatment depends on tumour biology and stage but commonly includes surgery, radiation therapy and systemic treatments.
Invasive Lobular Carcinoma (ILC)
Invasive Lobular Carcinoma (ILC) develops within the milk-producing lobules before invading surrounding breast tissue. ILC accounts for approximately 10–15% of invasive breast cancers.
Unlike ductal cancers, lobular cancers often grow in thin strands of cells rather than forming a distinct lump. This can make them more difficult to detect on mammography and physical examination.
ILC is also more likely to:
- Occur in multiple areas within the same breast
- Affect both breasts
- Be hormone receptor-positive
- Be HER2-negative
Although diagnosis may sometimes be delayed because of its growth pattern, outcomes are generally similar to IDC when diagnosed at comparable stages.
Inflammatory Breast Cancer
Inflammatory Breast Cancer (IBC) is a rare but aggressive type of breast cancer, accounting for approximately 1–5% of breast cancer diagnoses. Rather than forming a distinct lump, cancer cells block the lymphatic vessels within the skin of the breast, leading to inflammation.
Symptoms often develop rapidly over days or weeks and include:
- Significant breast swelling
- Redness
- Warmth
- Pain or tenderness
- Thickened ‘orange peel’ skin (peau d’orange)
- Flattening or inversion of the nipple
Because these symptoms resemble breast infection (mastitis), diagnosis can sometimes be delayed. Treatment usually begins with chemotherapy before surgery and radiation therapy.
Metastatic Breast Cancer
Metastatic breast cancer, also known as Stage IV breast cancer, occurs when cancer spreads beyond the breast tissue and nearby lymph nodes to distant organs.
Common sites of metastasis include:
- Bone
- Liver
- Lung
- Brain
Although metastatic breast cancer is generally not considered curable, advances in treatment mean many people now live for years with well-controlled disease. Treatment focuses on slowing disease progression, managing symptoms and maintaining quality of life.
Other Types of Breast Cancer
Several less common breast cancers also exist, including:
- Tubular carcinoma
- Mucinous (colloid) carcinoma
- Papillary carcinoma
- Medullary carcinoma
- Metaplastic breast carcinoma
- Paget disease of the nipple
Although uncommon, these cancers can behave differently and often require specialist assessment and individualised treatment planning.
Understanding Your Pathology Report
Following a biopsy or surgery, a pathologist examines the breast tissue and prepares a pathology report. This report contains important information that guides treatment recommendations.
A pathology report typically includes:
- Type of breast cancer
- Tumour size
- Tumour grade
- Hormone receptor status
- HER2 status
- Lymph node involvement
- Presence of lymphovascular invasion
- Surgical margin status
Together, these findings allow the multidisciplinary team, including surgeons, medical oncologists, radiation oncologists and other healthcare professionals, to develop an individualised treatment plan tailored to each person’s diagnosis.
Let’s explore each of these findings…
Breast Cancer Subtypes
Breast cancers can be further classified according to their pathological and biological characteristics. The terminology and classification used varies depending on whether the cancer is invasive or non-invasive.
A subtype describes the biological characteristics of the cancer cells rather than where the cancer started. These results help predict how the cancer is likely to behave and which treatments are most likely to be effective.
The pathology laboratory routinely tests for:
- Oestrogen receptors (ER)
- Progesterone receptors (PR)
- Human Epidermal Growth Factor Receptor 2 (HER2)
Hormone Receptor-Positive Breast Cancer
Approximately 70% of breast cancers are hormone receptor-positive. These cancers contain receptors that allow oestrogen and/or progesterone to stimulate cancer growth. Compared with other subtypes, they often grow more slowly and generally have an excellent prognosis when appropriately treated. Treatment commonly includes surgery followed by endocrine (hormone) therapy such as tamoxifen or aromatase inhibitors.
HER2-Positive Breast Cancer
HER2-positive breast cancers produce excessive amounts of the HER2 protein, causing cancer cells to grow more rapidly. Historically this subtype carried a poorer prognosis, however HER2-targeted therapies such as trastuzumab have dramatically improved survival. Treatment often combines surgery, chemotherapy, targeted therapy and radiation therapy where appropriate.
Triple Negative Breast Cancer
Triple Negative Breast Cancer (TNBC) lacks:
- Oestrogen receptors
- Progesterone receptors
- HER2 receptors
Because these receptors are absent, hormone therapy and HER2-targeted therapy are ineffective. TNBC tends to occur more commonly in younger women and those with BRCA1 mutations. It often grows more quickly but can respond very well to chemotherapy. Immunotherapy is also increasingly used in selected patients.
Triple Positive Breast Cancer
Triple positive breast cancer contains:
- Oestrogen receptors
- Progesterone receptors
- HER2 overexpression
These cancers may benefit from a combination of hormone therapy, HER2-targeted therapy and chemotherapy.
HER2-Low Breast Cancer
HER2-low breast cancer is a newer classification describing cancers with low levels of HER2 expression. Although these cancers are not considered HER2-positive, newer targeted therapies have expanded treatment options for some people with metastatic HER2-low breast cancer.
Breast Cancer Grading
Breast cancer grade describes how abnormal the cancer cells look under a microscope compared with healthy breast cells and provides an indication of how quickly the cancer is likely to grow. Unlike staging, which describes how far the cancer has spread, grading describes the characteristics of the cancer cells themselves. Pathologists assess features such as how different the cells look from normal breast cells, how they are arranged and how actively they are dividing.
Breast cancers are generally assigned a grade from 1 to 3:
- Grade 1 (low grade): cancers tend to look more like normal breast cells and are generally slower growing
- Grade 2 (intermediate grade): cancers have features between Grade 1 and Grade 3
- Grade 3 (high grade): cancers look more abnormal and tend to grow and divide more quickly
Tumour Size
The size of the primary tumour is one of the factors considered when determining the stage of breast cancer. It refers to the largest dimension of the invasive cancer, usually measured in millimetres or centimetres during imaging, biopsy or examination of the tissue removed during surgery.
As a general principle, a smaller tumour that remains confined to the breast may be associated with an earlier stage, while a larger tumour may contribute to a higher stage. However, tumour size alone does not determine the overall stage. The stage also takes into account whether cancer has spread to nearby lymph nodes or to distant parts of the body, along with other characteristics of the cancer.
It is also important to distinguish the size of the tumour from the stage of the cancer. A relatively small tumour can still have spread to lymph nodes or distant organs, while a larger tumour may remain confined to the breast.
Lymph Node Involvement
Breast cancer can spread from the breast to nearby regional lymph nodes, particularly those in the armpit (axilla). Assessing the lymph nodes is an important part of determining the stage of breast cancer. If no cancer cells are found in the regional lymph nodes that have been assessed, the cancer is described as node-negative. If cancer cells are identified in one or more regional lymph nodes, it is described as node-positive.
The number of lymph nodes involved, their location and the extent of cancer within the nodes can provide important information about the extent of the disease. Lymph node involvement does not automatically mean that breast cancer has spread to distant parts of the body. Regional lymph node involvement and distant metastasis are considered separately when determining the overall stage.
Lymph nodes may be assessed using imaging, a needle biopsy or during surgery. In some people, the sentinel lymph node, which is the first lymph node or group of nodes that lymphatic fluid from the breast is most likely to drain to, is examined to determine whether cancer cells have travelled beyond the breast.
Distant Spread/Metastasis
As part of breast cancer staging, doctors also assess whether cancer has spread beyond the breast and nearby lymph nodes to other parts of the body. This is known as distant spread or metastasis. When breast cancer cells break away from the primary tumour, they can travel through the bloodstream or lymphatic system to other areas of the body. If these cells establish a new tumour in another organ, this is called a secondary cancer or metastasis. Common sites of metastatic breast cancer include the bones, lungs, liver and brain, although breast cancer can spread to other parts of the body.
Breast cancer that has spread to distant organs is classified as Stage IV (metastatic or advanced breast cancer). This is different from cancer that has spread only to nearby regional lymph nodes. Regional lymph node involvement can occur in earlier stages of breast cancer and does not mean that the cancer has metastasised to distant organs.
Doctors may use imaging and other tests to assess whether distant spread is present, particularly when there are symptoms or other findings that suggest the cancer may have spread. The tests used depend on the individual circumstances. It is also important to understand that a secondary breast cancer remains breast cancer, even when it is found in another organ. For example, breast cancer that has spread to the bones is called metastatic breast cancer in the bone, rather than bone cancer.
Lymphovascular Invasion
Lymphovascular invasion (LVI) means that cancer cells have been found inside the small lymphatic vessels or blood vessels surrounding or within the breast tumour. These vessels are part of the body’s networks that carry lymph fluid and blood. Cancer cells can sometimes enter these vessels as they grow. Because lymphatic and blood vessels provide pathways through the body, the presence of LVI can indicate that cancer cells have gained access to these pathways.
The presence of LVI can provide additional information about the behaviour of the cancer and may be considered alongside other factors when assessing prognosis and planning treatment. However, LVI is not the same as metastatic breast cancer. Finding cancer cells within nearby lymphatic or blood vessels does not mean that cancer has necessarily spread to distant organs.
Not all breast cancers have LVI, and its presence or absence may be reported in the pathology results following a biopsy or surgery.
Surgical Margins
If breast cancer is removed during surgery, the pathologist examines the edges, or margins, of the tissue that has been removed. This helps determine whether cancer cells extend to the edge of the surgical specimen and whether the cancer appears to have been completely removed.
The margin may be described as:
- Clear or negative margin: No cancer cells are seen at the edge of the tissue that was removed. This means there is a margin of normal tissue between the cancer and the edge of the surgical specimen.
- Close margin: Cancer cells are close to the edge of the surgical specimen but do not reach it. Whether a close margin requires further treatment depends on the type of cancer, the type of surgery performed and other pathology findings.
- Positive or involved margin: Cancer cells extend to the edge of the surgical specimen. This may indicate that some cancer cells could remain in the breast and may lead to discussion about further surgery or other treatment.
The pathology report may also describe the distance between the cancer and the surgical margin, usually in millimetres. The significance of this distance depends on the type of breast cancer and the surgery performed.
Surgical margins are one part of the overall pathology assessment. Decisions about whether further treatment is needed are made by the treating team alongside other factors, such as the type and size of the tumour, lymph-node involvement, tumour grade and hormone receptor and HER2 status. A positive margin does not mean that the cancer has spread elsewhere in the body. It relates specifically to whether cancer cells are present at the edge of the tissue removed during surgery.
Breast Cancer Staging
Following diagnosis, breast cancer is assigned a stage to describe how far the cancer has spread. Staging helps guide treatment decisions and provides information about prognosis.
Stage 0 – Pre-invasive breast cancer: Abnormal cells are confined to the structure where they developed and have not invaded surrounding breast tissue. This includes ductal carcinoma in situ (DCIS). Classic lobular carcinoma in situ (LCIS) is generally considered a marker of increased future breast cancer risk rather than a conventional Stage 0 breast cancer.
Stage I – Early breast cancer: Stage I is the earliest stage of invasive breast cancer. Cancer cells have grown beyond the ducts or lobules into the surrounding breast tissue but remain within a relatively small area. The tumour size is less than 2cm with no cancer cells found in the nearby lymph nodes or other parts of the body.
Stage II – Early breast cancer: Stage II breast cancer is larger than Stage I and/or has spread to a small number of nearby lymph nodes. Stage II is divided into Stage IIA and Stage IIB:
- Stage IIA: This may involve:
- A tumour less than 2cm with cancer cells in 1–3 lymph nodes in the armpit
- A tumour 2–5cm with no lymph-node involvement, or
- No detectable tumour in the breast with cancer cells found in 1–3 lymph nodes in the armpit
- Stage IIB: This may involve:
- A tumour 2–5cm with cancer cells in 1–3 lymph nodes in the armpit, or
- A tumour larger than 5cm with no lymph-node involvement.
Stage III – Locally advanced breast cancer: Stage III breast cancer is a more advanced form of invasive breast cancer than Stage II. There is no detected spread to distant parts of the body, but the cancer may be larger, may have spread to several nearby lymph nodes, or may have spread into tissues around the breast, such as the skin, muscles or ribs. Some Stage II breast cancers may also be considered locally advanced.
- Stage IIIA:
- The tumour may be less than 5cm and have spread to 4–9 lymph nodes in the armpit, or to one or more lymph nodes under the breastbone.
- Alternatively, the tumour may be larger than 5cm and have spread to 1–9 lymph nodes.
- Stage IIIB:
- The tumour can be any size
- Has spread into tissues near the breast, such as the skin, muscles or ribs
- The cancer may or may not have spread to nearby lymph nodes, but there is no detected spread to distant parts of the body.
- Breast cancer involving the skin may include inflammatory breast cancer.
- Stage IIIC:
- The tumour can be any size
- Has spread to more extensive groups of lymph nodes, including 10 or more lymph nodes in the armpit, one or more lymph nodes above or below the collarbone, or lymph nodes in both the armpit and under the breastbone.
Stage IV – Advanced or metastatic breast cancer: Stage IV breast cancer, also called advanced, metastatic or secondary breast cancer, is breast cancer that has spread beyond the breast and regional lymph nodes to other parts of the body. This spread to a new location is called metastasis.
- The most common areas where breast cancer can spread include the bones, liver, lungs and brain, although it can spread to other organs
- Some people are diagnosed with metastatic breast cancer after previously being treated for an earlier-stage breast cancer, while for others, metastatic breast cancer is the first diagnosis of breast cancer (known as de novo metastatic breast cancer)
- Stage IV breast cancer can cause symptoms depending on where the cancer has spread, although some people may have no symptoms
- Treatment aims to control the growth and spread of the cancer, manage symptoms and maintain or improve quality of life
While metastatic breast cancer is not currently considered curable, treatment can control the cancer for some people for many years, and the cancer may respond to treatment or go into remission.
Key Takeaways
Understanding the different breast cancer characteristics can help make sense of the diagnosis and the treatment recommendations received. While terms such as tumour size, lymph node involvement, grade and stage can feel overwhelming, each provides important information that helps your healthcare team determine the most appropriate treatment approach.
It’s important to remember that breast cancer is not one single disease. Your treatment plan will be individualised based on the specific characteristics of the cancer, overall health and individual circumstances. If you have been diagnosed with breast cancer, your healthcare team can help you understand what your pathology and staging results mean for you. This knowledge can help you feel more informed and prepared as you navigate treatment and recovery.
References
Breast Cancer Network Australia. (n.d.). Understanding breast cancer. https://www.bcna.org.au/
Cancer Australia. (2024, November 16). Stages of breast cancer. Australian Government. https://www.canceraustralia.gov.au/cancer-types/breast-cancer/how-breast-cancer-diagnosed/stages-breast-cancer
Cancer Australia. (2024, November 16). Diagnosis of early breast cancer. Australian Government. https://www.canceraustralia.gov.au/cancer-types/breast-cancer/how-breast-cancer-diagnosed/diagnosis-early-breast-cancer
Cancer Australia. (2021, June 29). Stage at diagnosis by type (breast, prostate, colorectal, lung). National Cancer Control Indicators. https://ncci.canceraustralia.gov.au/stage-diagnosis/stage-diagnosis-type
Cancer Council Australia. (2024). Diagnosing breast cancer. https://www.cancer.org.au/types-of-cancer/breast-cancer/diagnosing-breast-cancer
Cancer Council Australia. (2021). Optimal care pathway for people with breast cancer (2nd ed.). https://www.cancer.org.au/assets/pdf/breast-cancer-2nd-edition
Disclaimer
This content is general in nature and provided for educational purposes only. It is not a substitute for individualised advice, diagnosis, or treatment. If you have concerns about your symptoms or health, consult a qualified healthcare professional.
