Which feature best distinguishes Li-Fraumeni syndrome (TP53 mutation) from hereditary retinoblastoma (RB1 mutation)?

Explanation

## Distinguishing Li-Fraumeni from Hereditary Retinoblastoma ### Key Clinical Difference **Key Point:** Li-Fraumeni syndrome (TP53 mutation) is characterized by a **broad spectrum of early-onset malignancies** across multiple organ systems, whereas hereditary retinoblastoma (RB1 mutation) has a **tissue-restricted phenotype** primarily affecting the retina and secondarily the bone/soft tissues. ### Comparative Table | Feature | Li-Fraumeni (TP53) | Hereditary Retinoblastoma (RB1) | |---------|-------------------|--------------------------------| | **Primary tumor** | Variable (breast, lung, colon, brain, leukemia, sarcoma) | Retinoblastoma (bilateral in 40%) | | **Age of onset** | Often <45 years; multiple primaries | Retinoblastoma <5 years; secondary sarcomas >10 years | | **Tumor spectrum** | Diverse (>10 different cancer types) | Retina + osteosarcoma/soft tissue sarcoma | | **Inheritance** | Autosomal dominant (germline TP53) | Autosomal dominant (germline RB1) | | **Hallmark** | **Multiple independent primary cancers** | **Ocular + skeletal malignancies** | ### Why This Matters **High-Yield:** TP53 is the "guardian of the genome" — loss of p53 function removes checkpoint control across all cell types, leading to **pan-cancer predisposition**. RB1 loss primarily affects G1/S checkpoint in retinal and bone cells, restricting the phenotype. **Clinical Pearl:** A 35-year-old woman with breast cancer, a 40-year-old sibling with colon cancer, and a parent with early-onset leukemia → suspect **Li-Fraumeni**. A 3-year-old with bilateral retinal masses and a 15-year-old sibling with osteosarcoma → suspect **hereditary retinoblastoma**. ### Mnemonic **TP53 = "Tumor Predisposition 53" (pan-cancer)** vs. **RB1 = "Retino-Bone 1" (tissue-restricted)** [cite:Robbins 10e Ch 7]