Objective: To study the impact of the retinoblastoma growth pattern (endophytic vs. exophytic) on the clinical and pathological features after primary enucleation.

Material and Method: A retrospective case series of 42 eyes of 41 patients who had pathologically confirmed retinoblastoma. The main outcome measures included demographics, laterality, international intraocular retinoblastoma (IIRC) group, vitreous seeding, neovascular glaucoma, choroid invasion, optic nerve invasion, metastasis, and survival.

Results: The median age at diagnosis was 30 months. Nineteen (46%) patients were males, and 17(41%) patients had bilateral retinoblastomas. Eight (19%) eyes were IIRC group C, 20 (48%) eyes were IIRC group D, and 14 (33%) eyes were IIRC group E. Nineteen (45%) tumors were endophytic, 14 (33%) were exophytic, and 9 (21%) were mixed. Choroid invasion was seen in 4 (21%) of the endophytic tumors, 5 (36%) of the exophytic tumors, and 8 (89%) of the mixed tumors (p=0.025). A mixed growth pattern was associated with massive choroid invasion in 5 (56%) of eyes. Neovascular glaucoma was seen in 5 (56%) of the mixed tumors (p=0.0376). Vitreous seeds were seen in 6 (67%) of the mixed tumors (p=0.0448). Optic nerve invasion as well as patients' age at diagnosis, gender, and tumor laterality had no correlation with tumor growth pattern. At a median follow up of 36 months, no single case had metastasis or was dead.

Conclusion: Exophytic tumors have higher risk of choroid invasion, while endophytic tumors have higher risk of vitreous seeding. The mixed tumor growth pattern is associated with more advanced IIRC group, more risk of neovascular glaucoma, and more risk of massive choroid invasion.