P37.11 Assessment of Plasma D-Dimer as a Predictive Biomarker for Treatment Response in Lung Cancer Treated with Radiation Therapy

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Plasma D-dimer, a sensitive biomarker for fibrinolysis in human body, is found raised in lung cancer patients. Increased D-dimer level is associated with large malignant tumor burden and poor clinical progression, hence changes in its concentration post treatment can be an indirect measure of changes in tumor burden, thus predicting treatment response. Treatment response assessment criteria are generally set upon radiological evidence of change in tumor volume. Radiation therapy to thorax causes regression of malignant lung tumor but with variable degree of surrounding fibrosis. This fibrosed tissue may obscure the actual volume of residual tumor (if any), thus giving false estimation of treatment response. A sensitive tumor biomarker may help to corroborate the findings of radiological imaging based response assessment. Between August 2018 and February 2020, previously untreated, histopathologically proven, fifty patients of locally advanced (stage IIIB, IIIC) and advanced (stage IV) non small cell lung cancer, presenting with pressing local symptoms, were included in this prospective, observational, single institutional study, after seeking informed consent. Pre treatment plasma D-dimer estimation was done in every patient before initiation of treatment with hypofractionated radiation therapy with 30 Gy, divided in 10 fractions (3 Gy per fraction), over a period of 10 days (5days in a week). Plasma D-dimer level of 0 to 500 ng/ml was considered normal. Treatment response was evaluated at 6 weeks after radiotherapy completion, by contrast enhanced CT scan of thorax and repeat plasma D-dimer evaluation was done at the same time. The correlation between pre and post treatment plasma D-dimer with respect to treatment response was evaluated by Wilcoxon Signed Rank Test, using IBM SPSS Statistics v26 software. P value < 0.05 was considered statistically signifiant. The median overall pre and post treatment plasma D-dimer levels were 1000 ng/ml (198 to 4800 ng/ml) and 1195 ng/ml (30 to 5694 ng/ml) respectively. Majority of patients having partial response (10 out of 14; 71.43%) had decrement in D-dimer levels post treatment with radiation therapy and these changes were found statistically significant (P = 0.023; pre RT vs post RT median D-dimer: 1021 ng/ml [200 to 3051 ng/ml] vs 490.5 ng/ml [30 to 2680 ng/ml]). Eleven out of 20 patients (55%) with stable disease had decrement in post treatment D-dimer levels, while the rest 9 patients (45%) with stable disease had further increment. Overall, these changes were not statistically significant (P = 0.661; pre RT vs post RT median D-dimer: 1062 ng/ml [305 to 4800 ng/ml] vs 1305.5 ng/ml [45 to 5694 ng/ml]). However, most of the patients having progressive disease (15 out of 16; 93.75%) had increment in their plasma D-dimer levels post treatment with a statistical significant change (P = 0.001; pre RT vs post RT median D-dimer: 827.5 ng/ml [198 to 2690 ng/ml] vs 2130 ng/ml [152 to 3412 ng/ml]). Plasma D-dimer possesses reasonably high prediction quotient for treatment response evaluation in lung cancer patients and may be used as a valuable, inexpensive biomarker to predict treatment response along with radiological imaging based response assessment.