This article aims to shed light on what causes breast cancer so that you can take control and lower your risk.

Breast cancer is a widely prevalent disease that affects millions of women worldwide. While it is known to be caused by the uncontrolled growth of abnormal cells in breast tissues, understanding the underlying causes can help raise awareness and promote prevention strategies. 

See also Breast Cancer and Smoking and How to Prevent Breast Cancer.

What is Breast Cancer?

Breast cancer is a type of cancer that starts in the breast. It can occur in both men and women, but it is much more common in women. 

Like any cancer, breast cancer happens when cells in the breast begin to grow out of control. These cells usually form a tumor that can often be seen on an X-ray or felt as a lump in the breast.

If the tumor is large, it may cause the breast to change shape or size. The skin over the breast may also become red or scaly, and there may be nipple discharge. 

Breast cancer is often first found by a woman herself when she notices these changes. However, some breast cancers are found on screening mammograms before they cause any symptoms.

According to the National Cancer Institute, most breast cancers are found in women 50 years old or more, but younger women can get breast cancer too. 

Types of Breast Cancer

According to the American Cancer Society, there are various types of breast cancer depending on the specific cells within the breast that get affected.

Ductal Carcinoma in Situ (DCIS)

DCIS is considered the earliest form of breast cancer and occurs when abnormal cells are found within the milk ducts but have not invaded surrounding tissues.

While it remains non-invasive at this stage, timely diagnosis and treatment are crucial to prevent its progression into invasive breast cancer. 

Invasive Ductal Carcinoma (IDC)

The most common type of breast cancer, IDC, starts in the milk ducts but eventually breaks through the duct walls and invades surrounding tissues. 

IDC accounts for approximately 80% of all diagnosed cases and can spread to other parts of the body if left untreated.

Lobular Carcinoma in Situ (LCIS)

Unlike DCIS, LCIS does not typically progress into invasive breast cancer itself; however, it increases a woman’s risk for developing invasive carcinoma in either breast later on. 

LCIS indicates an abnormal growth pattern within lobules (milk-producing glands) without spreading into nearby tissue.

Invasive Lobular Carcinoma (ILC)

ILC develops from lobules or glandular tissue and has distinctive characteristics compared to IDC. 

ILC tends to grow more diffusely throughout the breast rather than forming a distinct lump or mass, as seen in IDC.

Triple-Negative Breast Cancer (TNBC)

TNBC refers to tumors that lack estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). 

This type of breast cancer is more aggressive, less responsive to hormone therapy, and often requires alternative treatment approaches.

Hormone Receptor-Positive Breast Cancer

This type of breast cancer tests positive for either estrogen receptor (ER) or progesterone receptor (PR), indicating that these hormones may fuel the tumor. 

Targeted hormonal therapies can help block hormone receptors and prevent their expression.

Inflammatory Breast Cancer (IBC)

IBC is a rare but aggressive form of breast cancer that accounts for about 1-5% of all breast cancers. 

Unlike other forms of breast cancer, IBC does not typically present as a lump or tumor but manifests through visible changes in the skin, such as a rash, redness, swelling, warmth, inverted nipples, and pitted skin texture resembling an orange peel.

Closeup of pink badge ribbon on woman chest to support breast cancer cause.

Closeup of pink badge ribbon on woman chest to support breast cancer cause. Healthcare, medicine and breast cancer awareness concept.

What Causes Breast Cancer?

There’s no straight explanation as to what causes breast cancer since various factors have been shown to contribute to its occurrence.

These include:

1. Genetic Mutations 

Genetic mutations refer to alterations in our DNA sequence that can occur spontaneously or be inherited from our parents. These mutations can disrupt normal cellular functions and potentially drive the development of various diseases, including breast cancer.

The most well-known genetic mutations associated with breast cancer are those in the BRCA1 and BRCA2 genes. Individuals carrying these inherited gene mutations have a significantly higher lifetime risk of developing both breast and ovarian cancers compared to those without these mutations.

BRCA1 and BRCA2 are considered tumor suppressor genes, responsible for repairing damaged DNA or triggering cell death if repair is not possible.

When these genes acquire harmful mutations, their ability to function optimally is compromised, leading to an increased susceptibility to breast cancer.

2. Hormonal Imbalance

To comprehend the link between hormonal imbalance and breast cancer, it’s essential to understand the role hormones play in maintaining healthy breast tissue.

Estrogen and progesterone are crucial female hormones that regulate cell growth in the breasts. However, an imbalance in these hormones can disrupt this delicate equilibrium, increasing susceptibility to breast abnormalities and potential malignancy.

So, what can cause these imbalances?

a. Estrogen Dominance

Estrogen dominance occurs when there is an excess of estrogen relative to progesterone levels within the body. 

This condition can result from various factors such as stress, obesity, environmental toxins, or certain medications. 

Elevated estrogen levels have been associated with an increased risk of developing breast cancer due to its ability to stimulate cell division uncontrollably.

b. Menopausal Hormone Therapy (MHT)

Menopausal hormone therapy involves taking estrogen-only or combined estrogen-progestin supplements during menopause to alleviate symptoms like hot flashes or vaginal dryness. 

However, long-term MHT use has been linked to an elevated risk of developing breast cancer.

c. Polycystic Ovary Syndrome (PCOS)

Polycystic ovary syndrome is a common endocrine disorder characterized by hormonal imbalances leading to irregular periods, ovarian cysts formation, weight gain, and insulin resistance. 

Women with PCOS often experience higher estrogen levels and lower progesterone levels—factors that can increase their susceptibility to developing breast cancer later in life.

d. Obesity and Insulin Resistance

Obesity and insulin resistance contribute to hormonal imbalances, particularly by increasing estrogen production. 

This is because excess fat cells can convert various hormones, including testosterone, into estrogen, further disrupting the hormonal equilibrium. 

​​​​​​​This abnormal hormone activity may promote the growth of breast cancer cells.

3. Lifestyle Factors

a. Sedentary Lifestyle

Leading an inactive lifestyle has been associated with an increased risk of breast cancer. Contrary to this, engaging in moderate-intensity activities such as brisk walking or jogging for at least 150 minutes per week can help lower the risk.

b. Obesity and Excessive Weight Gain

Obesity is known to increase the risk of various types of cancers, including breast cancer.

The excess fat tissue produces estrogen hormones that can stimulate the growth of hormone receptor-positive breast tumors.

Maintaining a healthy weight through balanced nutrition and regular exercise is crucial for reducing this risk.

c. Diet and Nutrition

The food we consume plays a vital role in our overall well-being, including breast health. 

A diet rich in fruits, vegetables, whole grains, lean protein sources (such as poultry or fish), and low-fat dairy products provides essential nutrients that help reduce the risk of breast cancer. 

On the other hand, diets high in processed foods, red meat, saturated fats, and sugary beverages increase inflammation within the body and may promote tumor growth.

d. Alcohol Consumption

Studies have consistently shown that alcohol intake is directly linked to an increased risk of developing breast cancer. Even moderate alcohol consumption can elevate estrogen levels in women, thus increasing the risk of breast cancer.

According to the Breast Cancer Organization, women that consume 3 alcoholic drinks per week have a 15% increased risk of developing breast cancer compared to those that do not drink. And that’s not all; the risk increases by another 10% for each additional drink a woman consumes regularly each day. 

e. Smoking and Secondhand Smoke

Cigarette smoke contains more than 70 known carcinogens, including chemicals that damage DNA. This damage can lead to cancerous cell changes.

Smoking is estimated to increase the risk of breast cancer by 20 to 30 percent. The risk is even higher for women who start smoking as teenagers (below 17 years), having a 24% increased risk, while those who started between 17 ad 19 years have a 15% risk of breast cancer.

Additionally, secondhand smoke exposure also increases the risk of breast cancer, especially in premenopausal women.

Similar to active smoking, inhaling secondhand smoke exposes individuals to toxic chemicals that contribute to cellular damage leading to potential tumor formation.

Smoking also negatively influences the prognosis and survival rates of breast cancer patients: Smoking reduces the effectiveness of breast cancer treatments such as chemotherapy, radiation therapy, and hormone therapy.

For these reasons, smokers are more likely to experience disease recurrence after initial treatment compared to non-smokers, leading to poorer long-term outcomes.

Gender-related Risk Factors

  • Women: Being female is the most significant risk factor for developing breast cancer due to hormonal differences between genders. Estrogen exposure throughout a woman’s lifetime plays a more significant role in increasing susceptibility.
  • Men: Though it occurs less frequently, men are not immune to breast cancer. Male-specific risk factors include older age (above 60), family history, obesity, liver diseases like cirrhosis, or occupational exposure to radiation.

Diagnosis and Treatment of Breast Cancer



Regular self-examinations are an essential first step in detecting any abnormalities or changes in breast tissue. It involves observing and feeling one’s breasts for lumps, changes in size or shape, skin texture alterations, nipple discharge, or other unusual symptoms.

Ideally, every woman should self-examine their breasts regularly to help them familiarize themselves with their normal appearance, making identifying any changes or abnormalities easier. 

It also helps catch any lumps and masses earlier.

Clinical Examination

If you notice any concerning signs during self-examination, it is crucial to consult a healthcare professional who will conduct a clinical examination. They will assess your breasts manually, looking for any suspicious masses or abnormalities.

Imaging Tests

To further evaluate potential concerns identified during the clinical examination or screening programs, doctors often recommend imaging tests:

  • Mammogram: A mammogram uses low-dose X-rays to capture images of breast tissue from different angles. It can help detect tumors that may not be palpable during physical examinations.
  • Ultrasound: An ultrasound uses sound waves to create images of the breast tissue. It helps determine whether detected masses are solid (potentially cancerous) or fluid-filled (cysts).
  • MRI (Magnetic Resonance Imaging): In some cases where additional information is required, an MRI scan may be recommended as it provides detailed breast images using magnetic fields and radio waves.
Nurse Assisting Patient Undergoing Mammogram

Nurse Assisting Patient Undergoing Mammogram


If an abnormality is found through imaging tests or physical exams, a biopsy is performed to collect samples of suspicious tissues for laboratory analysis:

  • Fine-needle aspiration biopsy: A thin needle is used to extract cells from a lump or mass under local anesthesia.
  • Core needle biopsy: A slightly larger needle is used to remove a tissue sample from the suspicious area.
  • Surgical biopsy: In some cases, a surgical procedure may be required to remove an entire lump or a significant portion of it for further examination.

Laboratory Analysis

After obtaining tissue samples through biopsy, pathologists analyze them under a microscope. 

This process helps determine whether the cells are cancerous and provides essential information about tumor characteristics.


  • Surgery: Surgery plays a pivotal role in treating breast cancer by removing tumors and assessing the extent of its spread.
  • Radiation Therapy: Radiation therapy utilizes high-energy X-rays or other particles to kill or shrink cancer cells that may remain after surgery.
  • Chemotherapy: Chemotherapy involves using drugs to destroy rapidly dividing cells throughout the body, including cancer cells that have spread beyond the breasts.
  • Targeted Therapy: Targeted therapy focuses on specific characteristics found in breast cancer cells to disrupt their growth signals or promote immune system response against them.
  • Hormone Therapy: Hormone receptor-positive breast cancers can be treated with hormone-blocking medications that prevent estrogen or progesterone from fueling cancer growth.
  • Immunotherapy: Immunotherapy is an innovative approach that harnesses the body’s immune system to fight breast cancer cells.

Tips to lower your risk of breast cancer

  • Maintain a healthy weight
  • Engage in regular physical activity
  • Reduce alcohol consumption
  • Quit smoking
  • Breastfeed if possible
  • Be mindful of hormone therapy
  • Get regular screenings
  • Practice self-examination

Related Articles:

  1. Breast Cancer and the Reasons behind It’s Increasing Prevalence

  2. Top 11 Foods That Fight Breast Cancer

  3. Breast Cancer Awareness Month 2023: What You Should Know

  4. Can You Use Retinol While Breastfeeding?

Final Thoughts

Breast cancer is a complex disease with multiple risk factors that can increase the likelihood of its development.

While there are certain factors beyond our control, such as family history and genetic mutations, it is important to recognize the influence of modifiable risk factors like lifestyle choices and environmental exposures.

By maintaining a healthy weight, engaging in regular physical activity, limiting alcohol consumption, and avoiding exposure to harmful chemicals, individuals can reduce their risk of developing breast cancer.

Additionally, early detection through regular screenings and self-examinations remains crucial in improving prognosis and survival rates.

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