What Is Breast Cancer?
Breast cancer is a group of diseases characterized by the uncontrolled growth of abnormal cells in breast tissue—most commonly in the milk ducts (ductal carcinoma) or lobules (lobular carcinoma). Though it primarily affects women, men can also develop breast cancer.
It is the most common cancer in women worldwide and the second leading cause of cancer-related deaths. In the United States, approximately 1 in 8 women will be diagnosed with breast cancer during their lifetime. For 2025, an estimated 319,750 new invasive cases and around 42,680 deaths are expected.
Where Breast Cancer Starts
The breast is composed of lobules, ducts, fatty tissue, and connective tissue.
- Lobules produce milk — lobular carcinoma starts here
- Ducts carry milk to the nipple — most breast cancers are ductal carcinomas
- Nipple and areola — Paget’s disease of the breast begins in this area
- Stroma (fat and connective tissue) — tumors like phyllodes originate here
- Blood and lymph vessels — angiosarcomas begin in vessel linings
Other rare breast tumors include sarcomas and lymphomas, which are not typically classified as breast cancer.
How Breast Cancer Spreads
Cancer cells can spread via:
- Bloodstream
- Lymphatic system, which includes lymph nodes and vessels that drain fluid from breast tissue
Common areas for lymph node spread include:
- Axillary (underarm) nodes
- Internal mammary nodes (inside the chest)
- Supraclavicular/infraclavicular nodes (around the collarbone)
Presence in lymph nodes suggests a higher likelihood of metastasis, though not all such cases lead to distant spread.
Causes & Risk Factors
There is no single cause; rather, breast cancer develops due to a combination of genetic, hormonal, environmental, and lifestyle influences.
Non-Modifiable Risk Factors
- Age: Risk increases significantly after age 50
- Genetic mutations e.g. BRCA1, BRCA2, CHEK2
- Family history of breast or ovarian cancer
- Early menstruation (menarche) or late menopause
- Radiation exposure (e.g., treatment to chest during childhood)
Modifiable Risk Factors
- Alcohol consumption, obesity (particularly post-menopause), physical inactivity, and smoking
- Dense breast tissue, which can make tumors harder to detect
While about 30% of breast cancer cases are linked to genetic and hormonal factors, only ~5% are associated with inherited cancer syndromes.
Signs & Symptoms
- Early breast cancer may not show symptoms, but warning signs include:
- A painless lump in the breast or underarm
- Skin changes: dimpling, thickening, or redness
- Nipple changes: retraction or unusual discharge (sometimes bloody)
- Persistent pain, swelling in one breast, or swollen lymph nodes in the armpit
Early Detection & Diagnosis
- Early-stage breast cancer is often detected during routine screening before symptoms appear.
Screening Guidelines
- Average-risk women: Begin mammograms between ages 40–45; continue biennially or annually until age 74
- High-risk women: Start annual mammograms and MRI scans around age 30
Diagnostic Process
If abnormalities are found during screening or a clinical exam, follow-up may include:
- Breast imaging: ultrasound, mammogram, or MRI
- Biopsy: core needle or surgical, for tissue analysis
- Additional imaging: CT, PET, or bone scans to assess possible spread
Note: Breast self-exams are no longer recommended as a primary screening tool; instead, women are encouraged to be familiar with the normal look and feel of their breasts.
Treatment Overview
Breast cancer treatment is highly individualized, depending on the cancer’s type, stage, and the patient’s overall health and preferences.
Local Therapies
- Surgery: Lumpectomy or mastectomy
- Radiation therapy
Systemic Therapies
- Chemotherapy
- Hormonal therapy: for estrogen/progesterone receptor-positive (ER/PR+) cancers
- Targeted therapy: for HER2-positive cancers
- Immunotherapy: for certain advanced or triple-negative cases
A multidisciplinary approach is recommended, and patients are encouraged to seek second opinions.
Prognosis & Trends
- Death rates have declined by ~44% since 1989 due to early detection and improved treatments
- However, incidence is rising ~1% annually, particularly among women under 50, potentially due to lifestyle and reproductive factors
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