OBJECTIVES: Let-7 is a family of small non-coding RNAs regulating the expression 
of many genes that control important cellular activities. Let-7 is shown in 
vitro to sensitize cancer cells to platinum, but induce ovarian cancer 
resistance to paclitaxel. This study aims to investigate the effect of let-7a 
expression on survival outcomes of epithelial ovarian cancer (EOC) patients 
treated with different chemotherapy.
METHODS: Let-7a expression was measured with qRT-PCR in ovarian tumors of 178 
EOC patients who received platinum-based chemotherapy with and without 
paclitaxel after surgery. Survival analysis was performed to assess the effects 
of let-7a and chemotherapy on disease outcomes.
RESULTS: Let-7a expression was detectable in the EOC samples, but the expression 
was not associated with disease stage, tumor grade, histology and debulking 
results. Patients who responded to platinum with paclitaxel had significantly 
lower let-7a than those who did not. Survival analyses showed that patients with 
high let-7a had better survival compared to those with low let-7a when they were 
treated with platinum without paclitaxel. The hazards ratios (HRs) for death and 
disease progression were 0.52 (95% CI: 0.29-0.96) and 0.48 (0.26-0.89) for high 
let-7a when compared to low let-7a, respectively. However, when patients were 
treated with platinum and paclitaxel, high let-7a was associated with worse 
progression-free and overall survival. The HRs for death and disease progression 
were 3.87 (95% CI: 1.28-11.66) and 3.48 (95% CI: 1.25-9.67) for high let-7a when 
compared to low let-7a, respectively. Further studies showed that among patients 
with low let-7a, those treated with paclitaxel in addition to platinum survived 
better than those treated without paclitaxel [adjusted-HRs were 0.31 (95% CI: 
0.15-0.66) for death and 0.40 (95% CI: 0.22-0.75) for disease], while among 
those with high let-7a, the two types of treatment made no difference in patient 
survival.
CONCLUSIONS: The study suggests that the beneficial impact of the addition of 
paclitaxel on EOC survival was significantly linked to let-7a levels, and that 
miRNAs such as let-7a may be a useful marker for selection of chemotherapeutic 
agents in EOC management.