Prognostic Value And Predictive Value Of Let-7a For Accelerated Reproliferation During Radiotherapy In Lung Cancer

BackgroundLung cancer remains a major public health problem worldwide because of its high incidence,rapid progression,and poor outcome.The mainstay treatment for small cell lung cancer?SCLC?and advanced non-small cell lung cancer?NSCLC?has being chemoradiotherapy.Accelerated reproliferation during radiation is an important factor which result in radiotherapy failure.The identification of strategies that accurately reflect accelerated reproliferation during radiation would help in determining radiotherapy strategy,thus implement individualized treatment and improve long-term survival of patients.Material and methodsWe established A549 lung cancer xenograft model in nude mice,and part of the mice were sacrificed when the tumor diameter was about 1cm.¹⁸F-FLT PET-CT was carried out,and then transplanted tumor specimens,used quantitative real-time polymerase chain reaction?q PCR?and immunohistochemistry?IHC?to detect the expression level of let-7a and Ki-67.Other nude mice were randomly divided into three groups?the dose of radiation were 15Gy/5f?30Gy/10f?45Gy/15f,respectively?.Taking eye fissure blood before the treatment.The tumor growth were monitored by measuring the tumor size twice a week.Two mice from every group were used to evaluate tumor proliferation?tissue let-7a and Ki-67?using q PCR and IHC.Patients of lung cancer were prospectively enrolled from March 2014 to January2016.All patients were diagnosed of lung cancer pathologically.Patients were required to be staged by the seventh edition of American Joint Committee on Cancer?AJCC?,and those with inoperable stage III and stage IV were eligible.All patients received concurrent or sequential chemo-radiotherapy,or radiotherapy only.Peripheral blood was obtained before treatment and every week during radiotherapy,and then separated for serum.Quantitative real-time polymerase chain reaction?PCR?was utilized to detect the sequential expression level of let-7 in serum.Patients were followed up every 3 months within 2 years after treatment completion,then every 6 months after 2years.The primary endpoint of the study was the variation of serum let-7 level during radiotherapy.The second endpoint was the overall survival?OS?,which was measured from the date of diagnosis to the date of death.We used SPSS statistical software,version 13.0,for statistical analysis.ResultsIn A549 lung cancer xenograft model in nude mice,serum let-7a and tissue let-7a before radiotherapy were significantly correlated?P=0.013?.Serum and tissue let-7a before radiotherapy significantly correlated with Ki-67 of tumor tissue?P=0.045,0.018?.After 5,10,and 15 fractions of radiotherapy,serum let-7a and tissue let-7a of mice were significantly correlated?P=0.015,0.030,0.046,respectively?.After 5,10,and 15 fractions of radiotherapy,serum let-7a significantly correlated with tissue Ki-67 of corresponding periods?P=0.037,0.044,0.034,respectively?.Similarly,tissue let-7a also significantly correlated with tissue Ki-67 of corresponding periods?P=0.026,0.047,0.039,respectively?.Forty-two consecutive consenting patients were enrolled into this study.Twenty-one of them were taken blood samples before treatment and during the course of radiotherapy.Others were taken blood samples only before treatment.We found a strong correlation between serum let-7a and tissue Ki-67 before treatment?r=-0.571,P<0.001?.The tissue Ki-67 in patients with low serum let-7a were inclined to be higher.The difference of baseline serum let-7a among different differentiated subtypes was significantly?P=0.005?.The ability of baseline serum let-7a to predict prognosis was depicted by ROC curve.Areas under the curve?AUC?was 0.748.Patients with high level of baseline serum let-7a had significantly better 1-year OS?P=0.005?than patients with low level of baseline serum let-7a.For those patients with relatively low expression level of serum let-7a before radiotherapy,there was a peak of expression levels at the time point of week 3 during radiotherapy?the mean expression levels of let-7a at each week were 0.94,2.18,3.93,1.77,2.62,2.25 and 1.43,respectively?.However,for those patients with relatively high expression level of serum let-7a before radiotherapy,the expression levels were constantly downregulated,except slight discordance,at the time point of each week during radiotherapy compared with the original?the mean expression level were 7.42,1.80,0.44,0.79,1.77,1.97 and 1.53,respectively?.ConclusionsSerum let-7a is a prognostic factor,and could reflect the proliferation of tumor tissue reliably in lung cancer.Initial accelerated proliferation may exist in patients with relatively slow proliferation before radiotherapy,and late course accelerated reproliferation may exist in patients with relatively fast proliferation before radiotherapy.