Purpose: The aim of the present study was to detect the expression of P-glycoprotein (P-gp) and multi-drug resistance associated protein 1 (MRP1) in retinoblastoma tumors, and analyze the relationship between its expression, the clinico-pathological features and recurrence.

 Methods: P-gp and MRP1 expression in formalin-fixed paraffin-embedded retinoblastoma bearing ocular tissue sections from 26 patients were studied by immunohistochemistry assay, and the results were analyzed in correlation with clinico-pathological parameters. Patients were classified into two groups according to their treatment: with (n=16) and without (n=10) preoperative chemotherapy.

 Results: Six (23%) and 12 (46%) tumors were P-gp and MRP1 positive respectively. Three out of five tumors that presented P-gp had tumor invasion while MRP1 was positive in four tumors with invasion. Seven patients showed recurrence during follow-up time that P-gp and MRP1 were expressed in three and four of them, respectively. There was no correlation between protein expression and clinical outcomes as recurrence in this study.

 Conclusion: MRP1 and P-gp were intrinsically expressed in our study population. However, the results did not demonstrate significant association between P-gp and/or MRP1 positive expression and unresponsiveness to chemotherapy in Iranian retinoblastoma patients.

 Iranian Journal of Ophthalmology 201426(1):17-22 © 2014 by the Iranian Society of Ophthalmology