Causes, Symptoms & Diagnosis

Causes & Risk Factors

There is no single cause of breast cancer. It develops through a combination of genetic, biologic, hormonal, environmental, and lifestyle factors. The National Cancer Institute lists major risk factors including female sex, increasing age, inherited risk, breast density, obesity, alcohol use, and exposure to ionizing radiation. Inherited gene changes such as BRCA1 or BRCA2 also raise risk.^[4]

For HER2-positive disease specifically, the issue is that cancer cells have too many HER2 receptors or too many copies of the HER2 gene signal. HER2+ cancer is not contagious and is not caused by a single lifestyle choice — it develops when cell-growth controls stop working correctly.^[2]

Risk factors for developing breast cancer are different from why a cancer becomes stage 4. About 5–6% of women newly diagnosed with breast cancer in the U.S. have de novo metastatic disease — stage 4 from the start. Others begin at an earlier stage and later develop metastatic recurrence.^[1]

Signs & Symptoms

Early breast cancer symptoms can include a lump, skin changes, nipple changes, or breast swelling. Metastatic disease often causes symptoms tied to the distant organ involved.^[1]

Unusual fatigue is also common. Stage 4 breast cancer is often considered a chronic but treatable illness — usually not curable, but controllable for long periods. The goal is to slow growth, relieve symptoms, and improve quality of life. Some people live for years with well-controlled metastatic disease.^[1]

The Path to Diagnosis

Diagnosis usually starts with imaging. Imaging can identify abnormal areas, but a biopsy is the only sure way to diagnose breast cancer. Tissue is examined by a pathologist. Common methods are fine-needle aspiration, core biopsy, or excisional biopsy.^[5]

1. 01
   Self-Exam / Imaging

   A lump or abnormality is detected — often via self-exam or screening mammogram.
2. 02
   Biopsy

   Tissue is removed and examined to confirm cancer and check biomarkers (ER, PR, HER2).
3. 03
   Staging Imaging

   CT scans, bone scans, and PET scans identify whether and where the cancer has spread.
4. 04
   Biomarker Testing

   HER2 is tested by IHC or FISH; results guide targeted-therapy decisions.

All invasive breast cancers should be tested for HER2 on the biopsy or surgical sample. HER2 testing directly shapes treatment options.^[2] Biomarkers can change over time, which is why doctors sometimes repeat tissue testing if the cancer recurs or progresses.^[6]

Diagnostic Challenges

Symptoms of metastatic disease — fatigue, pain, shortness of breath, headaches — overlap with many other conditions. Some patients have no symptoms, or symptoms that don't match the textbook list.^[1]

The biology of the cancer can also shift over time. Hormone-receptor status may change, affecting treatment choices — another reason repeat testing is sometimes needed.^[6]

Connection to the Interview

Our interview subject was diagnosed after a self-exam lump. Her PET scan revealed cancer in the breast and liver simultaneously — a textbook example of de novo metastatic disease. She was also ER+/PR+, leading to a hysterectomy to remove hormonal fuel. Her remark "it should have been caught a lot sooner" echoes a system-level reality the research highlights: even with screening, aggressive cancers can outpace detection.

"I was never told I was cancer-free." — Interview Subject