Objective To observe the expression and relationship of high-mobility group A(HMGA)1, HMGA2, MIB-1 labeling index (LI) and let-7 in retinoblastoma (RB). Methods Forty-four RB samples were studied, including 11 poorly-differentiated samples, 33 well-differentiated samples; eight invasive and 36 non-invasive samples. The expression of HMGA1, HMGA2 and MIB-1 LI in RB were analyzed by immunohistochemitry. The HMGA1, HMGA2 were scored on a scale of 0 to high expression. 0: no expression; low: 1%-10%; medium: 11%-50%; high: ＞50%. The MIB LI were scored on a scale of 0 to high expression. 0: no expression; low: 1%-40%; high: ＞40%. Semiquantitative reverse transcription-polymerase chain reaction was used to assay the let-7 expression level: ge;80% showed no significantly decreased expression; 60%-79% showed medium decrease in expression; ＜60% highly decreased in expression. ResultsIn 44 RB samples, there were 14 cases with no HMGA1 expression (32%), 11 cases with low expression (25%), 10 cases with medium expression (23%), and nine cases with high expression (20%). Expression level of HMGA1 was significantly higher in poorly differentiated RB than in well-differentiated RB (chi;2=11.3,P＜0.01); however, no statistically significant difference was found between invasive tumors and noninvasive tumors (chi;2=5.9,P＞0.05). There were 11 cases with no HMGA2 expression (25%), 11 cases with low expression (25%), nine cases with medium expression (20%), and 13 cases with high expression (30%). Expression level of HMGA2 was significantly higher in poorly differentiated and invasive RB than in well-differentiated and noninvasive RB respectively (chi;2=20.9, 8.7;P＜0.05). There were 4 cases with no MIB-1 LI expression (9%), 18 cases with low expression (41%), and 22 cases with high expression (50%). Expression level of MIB-1 LI was significantly higher in poorly differentiated RB than in well-differentiated RB (t=5.2,P＜0.05). Higher expression of MIB-1 LI was found in invasive tumors than in noninvasive tumors, with no significant difference (t=-1.1,P＞0.05). Twenty-seven cases had no significantly decreased expression of let-7 (61%). There were eight cases with medium decreased expression (18%) and nine cases with highly decreased expression (21%). Correlation analyses revealed that MIB-1 LI expression significantly correlated with HMGA1and HMGA2 proteins (r=0.327, 0.602;P＜0.05). A significantly inverse correlation existed between let-7 expression and HMGA1, HMGA2 proteins and MIB-1 LI respectively (r=-0.247,-0.310,-0.392;P＜0.05). Conclusions Overexpression of HMGA1, HMGA2 and MIB-1 LI and down regulation of let-7 were demonstrated in RB. Supplying let-7 to RB cells can possibly inhibit HMGA1 and HMGA2 expression.