Breast Cancer Types Clinical Overview
I. The "On-Call" Snapshot
Clinical Significance in Malaysia: Breast cancer is the most common cancer among Malaysian women. A significant number, nearly half, are diagnosed at late stages (Stage III & IV), and we see it in younger women compared to the West. You will be clerking these patients in Surgical, Oncology, and even the Emergency Department.
High-Yield Definition: Breast cancer is a malignant proliferation of epithelial cells lining the ducts or lobules of the breast. Classification is based on histology (the cell type under the microscope) and molecular markers (the receptors on the cell surface).
Clinical One-Liner: Basically, it's not one disease. Think of it as a family of diseases, some slow-growing and hormonally driven, others aggressive and needing chemotherapy. Our job is to figure out which one we're dealing with.
II. Etiology & Risk Factors
Etiology: The proliferation is driven by genetic mutations (like BRCA1/2, TP53) and hormonal exposure that lead to uncontrolled cell growth.
Risk Factors (Malaysian Context):
Non-modifiable:
Female sex
Increasing age (though note our younger demographic)
Genetic predisposition (BRCA1/2 mutations are significant)
Family history of breast or ovarian cancer
Early menarche (<12 years) / Late menopause (>55 years)
Dense breast tissue on mammogram
Modifiable:
Nulliparity or late first pregnancy (>30 years)
Not breastfeeding
Obesity, particularly post-menopause
Alcohol consumption
Long-term use of combined hormone replacement therapy (HRT)
III. Quick Pathophysiology
In simple terms, normal breast cells respond to hormones like estrogen and progesterone to grow and function. When a cell's DNA is damaged, it can develop mutations. If these mutations affect genes that control cell growth, the cell can start dividing uncontrollably. This forms a tumour.
If the tumour cells stay within the duct or lobule, it's in-situ cancer (Stage 0).
If they break through the wall of the duct or lobule into surrounding breast tissue, it's invasive cancer. This is the crucial step that allows cancer to spread to lymph nodes and distant organs (metastasis).
The tumour's "personality" is determined by the receptors on its surface. This is the most important concept for you to grasp.
Hormone Receptors (ER/PR): If the cancer has Estrogen Receptors (ER) or Progesterone Receptors (PR), it uses the body's hormones to grow. This is a good thing for us, because we can block these receptors.
HER2: Human Epidermal Growth Factor Receptor 2 is a protein that promotes cancer growth. If a cancer overexpresses HER2, it's generally more aggressive. But again, we have targeted drugs for this.
Triple-Negative (TNBC): No ER, no PR, no HER2. These are aggressive, more common in younger women and those with BRCA1 mutations. We can't use hormone therapy or standard HER2 drugs, so chemotherapy is the mainstay.
IV. Classification of Breast Cancer
We classify breast cancer in two main ways that you must know. First by histology, then by molecular subtype.
A. Histological Classification (What the pathologist sees)
This is the traditional classification. It's about where the cancer started and what it looks like.
Non-Invasive Carcinoma (In-Situ)
Ductal Carcinoma In-Situ (DCIS): The most common non-invasive type. Malignant cells are confined to the breast ducts. It's considered a precursor to invasive cancer. We find this on mammograms as microcalcifications.
Lobular Carcinoma In-Situ (LCIS): Less common. Abnormal cells are in the lobules. It's more of a risk factor for developing invasive cancer in either breast, not a true precursor.
Invasive Carcinoma
Invasive Ductal Carcinoma (IDC): The workhorse of breast cancer, accounting for ~80% of cases. The cancer started in a duct and has broken out into the surrounding breast tissue. This is what you'll see most of the time.
Invasive Lobular Carcinoma (ILC): About 10-15% of cases. Tends to be more subtle on imaging, sometimes presenting as a thickening rather than a distinct lump. Often ER/PR positive.
Other less common types: Medullary, Mucinous, Tubular carcinomas. These often have a better prognosis. Inflammatory breast cancer is rare but very aggressive, presenting as a red, swollen breast, often without a palpable lump.
B. Molecular Subtypes (What drives the cancer)
This is how we decide on treatment. It's based on the ER, PR, and HER2 receptor status from the biopsy report. This is the most critical part for management.
Luminal A:
Receptors: ER/PR Positive, HER2 Negative.
Proliferation (Ki-67): Low.
Features: The most common type (~70%). It's slow-growing, responds very well to hormone therapy, and has the best prognosis.
Luminal B:
Receptors: ER/PR Positive, HER2 Positive or Negative.
Proliferation (Ki-67): High.
Features: Faster growing than Luminal A. Responds to hormone therapy but often requires chemotherapy due to its higher proliferation rate. If HER2 positive, it also needs anti-HER2 therapy. Prognosis is good, but less favorable than Luminal A.
HER2-Enriched:
Receptors: ER/PR Negative, HER2 Positive.
Proliferation (Ki-67): High.
Features: Aggressive and fast-growing. The prognosis was historically poor but has been dramatically improved by anti-HER2 targeted drugs (like Trastuzumab).
Triple-Negative (TNBC):
Receptors: ER Negative, PR Negative, HER2 Negative.
Proliferation (Ki-67): High.
Features: Accounts for about 15% of cases. This is the most aggressive subtype. It doesn't respond to hormonal or standard anti-HER2 therapies, so the mainstay of treatment is chemotherapy. It has higher rates of recurrence and is more common in younger patients and those with BRCA1 mutations.
Clinical Pearl: When you get a histology report, don't just read the top line. Immediately look for the ER, PR, and HER2 status. This tells you what kind of fight you're in for and what weapons you can use.
V. How to Present to Your Senior
When presenting a new case, be systematic.
"Dr, for review please. This is Puan Lim from the clinic, a 55-year-old woman who presented with a right breast lump. Clinically, there is a 3cm, hard, irregular lump in the upper outer quadrant with axillary lymphadenopathy. The biopsy report confirms an Invasive Ductal Carcinoma, Grade 2. Importantly, the immunohistochemistry shows it is ER positive, PR positive, and HER2 negative. My initial assessment is a Luminal A subtype of breast cancer. I have completed the staging workup and would like to discuss the plan for surgery and adjuvant therapy."
VI. Summary & Further Reading
Top 3 Takeaways:
Breast cancer is not one disease. The key distinction is Invasive vs. Non-Invasive.
The Molecular Subtype (Luminal A/B, HER2-Enriched, Triple-Negative) is the most important factor that dictates the treatment plan.
Always check the ER, PR, and HER2 status on every pathology report. It's your guide to management.
Key Resources:
Management of Breast Cancer (3rd Edition) - Ministry of Health Malaysia Clinical Practice Guidelines. (Always refer to the latest version on the MOH website).
UpToDate: Search for "Overview of breast cancer" and "Prognostic and predictive factors in breast cancer".
Amboss: Search for "Breast Cancer". A good, quick reference.
