A 2-year-old boy presents with leukocoria and strabismus. Fundoscopy reveals a white intraocular mass with calcification. Regarding retinoblastoma, all of the following are TRUE EXCEPT:

## Retinoblastoma: Epidemiology, Genetics, and Presentation ### Key Clinical Features **Key Point:** Retinoblastoma is the most common intraocular malignancy in children, with an incidence of 1 in 15,000–20,000 live births. ### Presentation and Detection **High-Yield:** The classic presenting signs of retinoblastoma include: 1. **Leukocoria** (white pupil reflex / cat's eye reflex) — most common presenting sign (~60% of unilateral cases) ✅ TRUE 2. **Strabismus** (~20% of unilateral cases) 3. **Eye pain and vision loss** — less common at presentation **Clinical Pearl:** Leukocoria is the most frequent sign in unilateral disease and should always prompt immediate dilated fundoscopy and referral to a pediatric ophthalmologist. ### Genetic Basis **Key Point:** RB1 gene mutations follow an **autosomal dominant** inheritance pattern with **incomplete penetrance** (~90%) and **variable expressivity**. ✅ TRUE (Option D) - **Hereditary retinoblastoma:** ~40% of all cases - **Bilateral disease: ~80–90% of hereditary cases** (NOT 40%) - Unilateral disease: ~10–20% of hereditary cases - **Sporadic retinoblastoma:** ~60% of all cases (somatic mutations, almost always unilateral) ### The FALSE Statement — Option C **High-Yield:** Option C states that "bilateral disease occurs in approximately 40% of hereditary cases." This is **FALSE**. According to standard references (Shields & Shields, Kanski's Clinical Ophthalmology, and Robbins Pathology), **bilateral retinoblastoma occurs in approximately 80–90% of hereditary (germline) cases**, not 40%. Conversely, ~40% of ALL retinoblastoma cases are hereditary — this is a common source of confusion. Bilateral disease is virtually always due to a germline RB1 mutation. ### Stage at Presentation **High-Yield:** The stage at presentation varies by geography: | Region | Metastatic Disease at Presentation | Cure Rate | | --- | --- | --- | | Developed countries (USA, Europe) | <5% | >95% | | Developing countries (India, Africa) | 40–70% | <50% | **Clinical Pearl:** Option B (metastatic disease >80% in developing countries) is an overstatement but is within the range of some reports from sub-Saharan Africa; however, the consensus figure cited in most standard texts is 40–70%, making Option B a plausible distractor. Option C, however, contains a clear, well-established factual error. ### Summary of Options | Option | Statement | Verdict | |--------|-----------|---------| | A | Leukocoria is most common sign in unilateral disease | TRUE | | B | Metastatic disease >80% in developing countries | Overstated but debatable | | C | Bilateral disease in ~40% of hereditary cases | **FALSE — it is ~80–90%** | | D | RB1 inherited as autosomal dominant with incomplete penetrance | TRUE | [cite: Kanski's Clinical Ophthalmology 9e; Shields & Shields Intraocular Tumors 3e; Robbins & Cotran Pathologic Basis of Disease 10e Ch 10]