Breast Cancer: Understanding the Science and Its Impact
- MedSCi Club
- Mar 20
- 9 min read
Updated: Mar 21
Author(s): Chidchaya Wankaew
What is breast cancer?
Breast cancer is the most common cancer in women in the UK, with around 56,800 new cases and approximately 11,500 deaths each year. It is estimated that 1 in 7 women will be diagnosed with breast cancer in their lifetime, making it a significant public health concern.
Cancer, in general, refers to the uncontrolled growth and division of abnormal cells in the body. These cells can form a mass known as a tumour and, in some cases, spread to other parts of the body (metastasis). In breast cancer specifically, this abnormal cell growth occurs in breast tissue, most commonly originating in the ducts (which carry milk) or lobules (which produce milk).
Understanding breast cancer is important because early detection greatly improves outcomes. Being aware of the risk factors, signs, and available screening methods allows individuals to seek medical attention promptly, increasing the chances of effective treatment and survival.
Risk factors
Risk factors are aspects of personal behaviour, lifestyle, environmental exposure or inherited characteristics that increase an individual’s risk of developing a disease. Different cancers have different risk factors and having one or more, among the many risk factors of breast cancer, does not guarantee that someone will get breast cancer. Likewise, breast cancer can occur despite the absence of these risk factors.
Age
The likelihood of breast cancer increases with age. In many populations, about 75% of breast cancers occur in women over the age of 50, as stated by Breast Cancer Network Australia (BCNA).
Personal history of cancer
Patients who have had breast cancer are more likely to develop breast cancer again in the same or other breast than someone who has never had breast cancer.
Family History
Having first degree relatives (mom or sister) with breast cancer increases risk of developing breast cancer up to 2 or even 3 times, according to the American Cancer Society.
Female gender
Being female is the strongest single risk factor as breast cancer is far more common in women than in men.
Genetic factors
For example, inherited mutations account for an important minority of breast cancer cases. A mutation in genes that regulate cell division can lead to uncontrolled cell growth, resulting in several cancers including breast cancer. A common example is inherited Breast Cancer Gene (BRCA1 or BRCA2) which significantly elevates lifetime risk of breast cancer and is responsible for around 5-10% of cases (Majeed et. al 2014). Others include mutations in PALB2, CHEK2, TP53.
Exogenous hormone exposure
Certain hormonal contraceptives are found to increase risks of breast cancer, though by very small amounts. An example are hormonal birth controls, containing oestrogen that prevent growth and maturation of eggs in the ovaries by suppressing follicle-stimulating hormone (FSH). Hormone replacement therapy (HRT) is often used by individuals transitioning or to reduce post-menopausal symptoms, with its associated risks increasing with longer use and declining after stopping HRT. The NHS reports that there are about 5 additional cases per 1,000 women over 5 years of use.
Radiation
Exposure to ionising radiation (especially from a young age before puberty) is known to increase susceptibility to many types of cancer. Sources of radiation include diagnostic tests such as x-rays and CT scans and treatments such as radiotherapy. The risk increases with dosage size hence diagnostic imaging like mammograms that use low doses overall benefit screening more than they contribute to risk.
Obesity
Obesity is linked with increased risk of breast cancer, particularly in post-menopausal women due to higher oestrogen produced from adipose tissue. Body mass index (BMI) is a standard measure that uses height and weight to determine whether an individual is at a healthy weight. Maintaining a healthy weight reduces the risk of 13 different types of cancer including breast cancer.
Alcohol
Higher consumption increases risk of breast cancer. Women who consume 1 alcoholic drink daily have around 7-10% higher risk than nondrinkers and the associated risks are greater at higher levels of intake, where risks increase by around 7% with each extra alcoholic drink per day based on the National Cancer Institute (NCI).
Smoking
Smoking tobacco is associated with a small increased risk of breast cancer, although evidence is not as strong or consistent as other lifestyle risk factors like alcohol or obesity.
Signs of breast cancer
Understanding the possible signs of breast cancer supports early diagnosis and effective management. Although many breast symptoms are benign (not cancerous), persistent or unexplained breast changes should always be reviewed by a healthcare professional. Common signs and symptoms of breast cancer include:
An unusual lump or mass in the breast or underarm region. It may be hard or firm and may or may not be painful.
Changes in shape, size, or symmetry of the breast, including unexplained enlargement, shrinkage, or visible distortion.
Changes to breast skin such as dimpling, puckering, generalized swelling, or a texture resembling orange peel (peau d’orange).
Nipple changes, including inversion (retraction), unusual discharge (especially bloody or clear if not breastfeeding), and lasting rashes or thickening around the nipple or areola.
Persistent pain or discomfort in any area of the breast or nipple not explained by benign causes.
Swelling or lumps in nearby lymph nodes, particularly under the arm or near the collarbone.
In more advanced cases, systemic symptoms such as unexplained weight loss or persistent bone or abdominal pain may arise.
 Nipple Retraction |  Skin dimpling (Peau D’orange) |  Rashes on breast skin |
Screening for breast cancer
Screening plays an important role in the early detection of breast cancer, often before symptoms become noticeable. Women are advised to regularly check their breasts for any unusual changes, such as lumps, skin changes, or nipple abnormalities.
In addition to self-examination, routine screening is recommended for certain groups. Women over the age of 50 are typically advised to undergo mammography on a regular basis (annually or every two years). Earlier screening may be recommended for individuals with a family history of breast cancer or known genetic mutations such as BRCA1 or BRCA2. Early detection through screening significantly improves the likelihood of successful treatment.
Investigations
Investigations for breast cancer are divided into screening and diagnostic tests. Screening tests are generally less invasive and used to identify individuals who may have breast cancer, but they do not provide a definitive diagnosis. Diagnostic tests, on the other hand, are used to confirm the presence of cancer and provide further information such as staging and subtype.
The gold standard for diagnosing breast cancer is the Triple Assessment, which combines three key components:
1. Breast Examination A clinical examination involves inspecting and palpating the breast to identify any lumps or abnormalities. Breast tumours are typically firm, painless, and immobile. The lymph nodes, particularly in the axillary region, are also assessed for enlargement.
2. Mammography Mammography is an X-ray imaging technique used to detect abnormalities within breast tissue. It can identify masses or suspicious areas but cannot definitively determine whether a tumour is cancerous.
3. Biopsy A biopsy is the confirmatory test for breast cancer. A sample of tissue is taken and analysed histologically to determine whether cancer is present and to identify its subtype and stage.
Core biopsy (gold standard): A needle is guided (often using ultrasound) to obtain a tissue sample, allowing assessment of cell structure and architecture.
Sentinel lymph node biopsy: The first lymph node receiving drainage from the breast is removed and examined for metastasis. If cancer is present, further lymph node removal (axillary lymphadenectomy) may be required.
 Patterns for palpation of the breast |  Mammography of the breast |  Ultrasound-guided core biopsy |
Treatment of Breast Cancer
Breast cancer treatment is divided into four main categories, and the approach depends on the subtype and stage of the cancer, which are determined through biopsy and histological analysis.
1. Hormonal Therapy This is often the first-line treatment with relatively fewer side effects. It is used in cancers that are hormone receptor-positive (e.g. ER-positive). Drugs such as Tamoxifen or aromatase inhibitors are commonly used. HER2-positive cancers may be treated with targeted therapy such as Trastuzumab. Hormonal therapy is not effective in triple negative breast cancer.
2. Chemotherapy Chemotherapy uses drugs to destroy cancer cells and may be given before surgery (neoadjuvant) to shrink tumours or after surgery to eliminate remaining cancer cells. While effective, it is associated with significant side effects.
3. Radiotherapy Radiotherapy uses targeted radiation to kill cancer cells and is commonly used after surgery to reduce the risk of recurrence.
4. Surgical Excision Surgery involves removing cancerous tissue and may be necessary depending on tumour size and spread.
Breast Conserving Surgery (BCS): Removes the tumour while preserving as much breast tissue as possible.
Total Mastectomy: Removal of the entire breast, often used in more advanced or aggressive cases.
Axillary Lymphadenectomy: Removal of lymph nodes if cancer has spread to them.
Although surgery was once the primary treatment, newer therapies have reduced its use in some early-stage cases. However, surgical treatment can have psychological impacts due to changes in appearance.
Remission
Remission refers to the period after treatment when the signs and symptoms of cancer are reduced or no longer detectable. However, cancer is not always completely eradicated, and there remains a risk of recurrence.
For this reason, patients are advised to continue regular follow-up and screening after treatment to monitor for any return of the disease.
Diving deeper
Breast cancer most commonly originates in either the ducts or lobules of the breast. The lobules are responsible for producing milk, while the ducts carry milk to the nipple. Depending on where the abnormal cell growth begins, breast cancer is classified as either ductal or lobular carcinoma.
To better understand and treat breast cancer, tumours are further classified into subtypes based on specific biological markers. These include oestrogen receptors (ER), progesterone receptors (PR), Human Epidermal Growth Factor Receptor 2 (HER2), and the proliferation rate of the cancer (Ki-67), which reflects how quickly the tumour is growing. Identifying these markers is essential in determining both prognosis and the most effective treatment plan.
Based on these markers, breast cancer can be classified into four main subtypes:
Luminal A This subtype is ER-positive, HER2-negative, and has a low proliferation rate (Ki-67 below 14%). It is typically a low-grade, slow-growing cancer with a good prognosis and a lower risk of relapse. Luminal A cancers respond well to hormonal therapies such as Tamoxifen or aromatase inhibitors.
Luminal B Luminal B cancers are also ER-positive and HER2-negative, but have a higher proliferation rate (Ki-67 above 14%). They are generally more aggressive than Luminal A and have a slightly worse prognosis. While they still respond to hormonal therapy, chemotherapy is often required as well.
HER2-positive This subtype is ER-negative and HER2-positive, with a high proliferation rate. It is typically aggressive and fast-growing. However, targeted therapies such as Trastuzumab have significantly improved outcomes for patients with HER2-positive breast cancer.
Triple Negative Breast Cancer (TNBC) This subtype lacks ER, PR, and HER2 receptors. It is often the most aggressive form and is associated with a poorer prognosis. However, it is less common compared to other subtypes. As it does not respond to hormonal or HER2-targeted therapies, treatment options are more limited.
In addition to subtype classification, breast cancer is also staged using the TNM system, which describes how far the cancer has developed and spread. Staging is based on tumour size (T), lymph node involvement (N), and distant metastasis (M). In general, higher stages are associated with a worse prognosis and lower survival rates.
Tumour Size (T) | Nodal Involvement (N) | Distant Metastases (M) |
This describes the size of the tumour and whether it has spread to nearby structures such as the chest wall or skin.
| This refers to whether the cancer has spread to nearby lymph nodes, particularly in the axillary (underarm) region.
| This indicates whether the cancer has spread to distant organs.
|
For example, a patient with a 3 cm tumour, involvement of 1 lymph node, and no distant metastases would be staged as T2N1M0.
Metastasis refers to the spread of cancer cells from the original (primary) tumour to other parts of the body. Cancer cells can break away from the primary tumour, travel through the blood or lymphatic system, and form new tumours in distant organs.
Breast cancer commonly metastasises to the bone, lungs, liver, and brain. This pattern is partly due to the rich blood supply and vascular networks in these organs, which make it easier for circulating cancer cells to enter and establish secondary tumours. Additionally, the lymphatic system plays a key role in spreading cancer cells from the breast to nearby lymph nodes and beyond.
Lymph nodes themselves are an important part of the immune system. They contain white blood cells and help filter lymph fluid, trapping harmful substances such as bacteria and cancer cells. However, this also makes them a common site for early cancer spread.
References
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McCarthy AM, Friebel-Klingner T, Ehsan S, et al. Relationship of established risk factors with breast cancer subtypes. Cancer Med. 2021;10(18):6456-6467. doi:10.1002/cam4.4158
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