Which feature best distinguishes BRCA1-associated breast cancer from BRCA2-associated breast cancer in terms of tumor biology and clinical presentation?

Question

Accepted Answer

A. BRCA1 tumors are typically triple-negative (ER−, PR−, HER2−), whereas BRCA2 tumors are often hormone receptor–positive. ## Distinguishing BRCA1 from BRCA2 Tumors

### Key Molecular Difference

**Key Point:** BRCA1-associated breast cancers are characteristically **triple-negative** (estrogen receptor–negative, progesterone receptor–negative, HER2-negative), reflecting a distinct molecular phenotype. BRCA2-associated breast cancers are more often **hormone receptor–positive**, resembling sporadic luminal breast cancers.

### Comparative Table

| Feature | BRCA1-Associated | BRCA2-Associated |
|---------|------------------|------------------|
| **ER/PR status** | Predominantly negative | Often positive |
| **HER2 status** | Negative | Variable |
| **Molecular subtype** | Triple-negative (basal-like) | Luminal A/B or HER2+ |
| **Grade** | High grade (poorly differentiated) | Variable |
| **Age of onset** | Younger (<50 years, often <40) | Younger but slightly older than BRCA1 |
| **Male breast cancer** | Rare (<5%) | Common (5–10%) |
| **Ovarian cancer risk** | High (40–50%) | Lower (10–20%) |
| **Pancreatic cancer risk** | Moderate (2–3%) | Moderate (2–7%) |
| **Prostate cancer risk (males)** | Low | Elevated |
| **Inheritance** | Autosomal dominant | Autosomal dominant |

### Why This Matters

**High-Yield:** BRCA1 loss impairs homologous recombination repair (HR) and also functions in transcriptional regulation and cell-cycle checkpoint control. The loss of these pleiotropic functions drives a **basal-like, triple-negative phenotype**. BRCA2 is primarily an HR repair gene; its loss does not enforce a specific hormone receptor phenotype, so BRCA2 tumors resemble sporadic breast cancers more closely.

**Clinical Pearl:** A 35-year-old woman with **triple-negative breast cancer** and a strong family history of breast/ovarian cancer → **BRCA1 mutation likely**. A 50-year-old man with **hormone receptor–positive breast cancer** and a family history of breast cancer → **BRCA2 mutation likely**.

### Mnemonic

**BRCA1 = "Basal-like, Receptor-negative, Cancer-aggressive"** vs. **BRCA2 = "Breast-cancer-2, (also) male breast cancer"**

[cite:Robbins 10e Ch 7]

Answer

B. BRCA1 mutations confer higher lifetime breast cancer risk (70%) compared to BRCA2 (45%)

Answer

C. BRCA2 mutations are associated with male breast cancer, whereas BRCA1 mutations rarely cause male breast cancer

Answer

D. BRCA1 mutations are autosomal recessive, whereas BRCA2 mutations are autosomal dominant

Which feature best distinguishes BRCA1-associated breast cancer from BRCA2-associated breast cancer in terms of tumor biology and clinical presentation?

Explanation

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