A 3-year-old girl from Delhi with unilateral retinoblastoma (right eye, International Classification Group C) has completed 3 cycles of neoadjuvant intravenous chemotherapy (vincristine, etoposide, carboplatin). MRI shows partial regression of the mass (50% reduction in volume), but the tumour remains intraocular with no extraocular extension. The child has light perception in the affected eye. What is the most appropriate next step in management?

Explanation

## Clinical Scenario Analysis A 3-year-old with Group C unilateral intraocular retinoblastoma showing **partial response (50% volume reduction)** after 3 cycles of neoadjuvant chemotherapy (VEC: vincristine, etoposide, carboplatin), with retained light perception and no extraocular extension, is a candidate for **globe-sparing combined modality consolidation therapy**. ## Why Combined Focal Therapy + Radiation is Correct **Key Point:** International Classification Group C retinoblastoma (focal or diffuse vitreous/subretinal seeding, but confined to the globe) is managed with a globe-preserving multimodal approach. After partial response to neoadjuvant chemotherapy, the standard consolidation is **focal therapy (laser photocoagulation or cryotherapy) combined with EBRT or brachytherapy** to sterilize residual tumour and seeds. This is supported by guidelines from the Children's Oncology Group (COG) and major retinoblastoma centres (Shields & Shields, *Intraocular Tumors*, 3rd ed.; Murphree, *Ophthalmology Clinics of North America*). **High-Yield:** Eye salvage rates for Group C retinoblastoma with multimodal therapy (chemotherapy + focal therapy ± radiation) range from **70–85%** in published series (Shields et al., *Ophthalmology* 2004; Friedman et al., *J Clin Oncol* 2000). Enucleation is **not** the next step when the tumour is responding and the eye retains light perception. ### Consolidation Strategy for Group C After Partial Chemotherapy Response | Modality | Indication | Notes | |----------|-----------|-------| | **Laser photocoagulation** | Residual tumours <3 mm, away from disc/macula | Thermal destruction of residual foci | | **Cryotherapy** | Anterior retinal tumours, subretinal seeds | Freeze-thaw necrosis | | **EBRT** | Large residual mass, diffuse vitreous seeding | 40–45 Gy fractionated; risk of secondary malignancy | | **Brachytherapy (episcleral plaque)** | Solitary residual mass ≤15 mm | Lower systemic/contralateral radiation exposure; preferred in young children | **Clinical Pearl (KD Tripathi / Shields):** In young children, **brachytherapy is preferred over EBRT** when feasible, to reduce radiation dose to the developing orbit, contralateral eye, and brain, and to lower the risk of secondary malignancies (especially relevant in heritable RB). ### Why Each Distractor is Incorrect - **Option A (Enucleation):** Reserved for: (i) no light perception / blind painful eye, (ii) failure of all globe-sparing modalities, (iii) extraocular extension, (iv) rubeosis iridis with secondary glaucoma. A 50% response with retained light perception and no extraocular disease does **not** meet enucleation criteria. - **Option B (3 more cycles of chemotherapy alone):** Continuing systemic chemotherapy without consolidation focal/radiation therapy is not standard after a partial response. Additional chemotherapy cycles without local consolidation leave residual disease inadequately treated and increase cumulative toxicity. - **Option D (Intravitreal melphalan):** Intravitreal chemotherapy is indicated specifically for **vitreous seeding** refractory to systemic chemotherapy, or as salvage after EBRT failure — not as primary consolidation for a partially responding Group C tumour mass. ## Treatment Algorithm for Group C Retinoblastoma (Post-Chemotherapy) ``` Group C RB → Neoadjuvant VEC (3–4 cycles) ├── Complete response → Focal therapy ± brachytherapy ├── Partial response → Focal therapy + EBRT or brachytherapy ← THIS CASE └── No response / progression → Intravitreal chemo (if vitreous seeds) or Enucleation ``` **Key Point:** The evidence-based standard for Group C retinoblastoma with partial chemotherapy response is consolidation with **focal therapy combined with EBRT or brachytherapy**, achieving 70–85% eye salvage rates (Shields et al., *Ophthalmology* 2004). Enucleation is a last resort, not the next step in a responding eye with retained vision.