The role of pre- and post-treatment PET-BT parameters in predicting pathological complate response in patients with gastric cancer receiving neoadjuvant chemotherapy

Objective: The standard treatment approach for locally advanced gastric cancer is surgery following neoadjuvant chemotherapy (NACT). This study aimed to investigate the role of pre- and post-treatment positron emission tomography computed tomography (PET-CT) parameters in predicting pathological complete response (PCR) in patients with gastric cancer who received neoadjuvant chemotherapy. Materials and Methods: This study included a total of 75 patients who were diagnosed with gastric adenocarcinoma, received neoadjuvant chemotherapy, and were followed up with pre- and post-treatment PET-CT between January 01, 2014, and September 01, 2024, in the Medical Oncology outpatient clinic of Dicle University Faculty of Medicine Hospital. The demographic data, clinicopathological characteristics, various laboratory parameters, and PET-CT images of the patients were examined based on the information in the hospital records. Results: A total of 75 patients were included in the study. 78.7% of the patients were male, 21.3% were female and the mean age was 57.60 ± 11.75 years. Histologically, 64% of the cases were classified as intestinal, 36% as diffuse type. 94.7% of all patients underwent positron emission tomography-computed tomography (PET-CT) imaging before neoadjuvant chemotherapy (NACT), 73.3% after treatment ,68% underwent PET-CT imaging both before and after treatment. In PET-CT evaluations, the median metabolic tumor volume (MTV) 32.7, maximum standardized uptake value (SUVmax) 9.4, total lesion glycolysis (TLG) 182.2 and mean standardized uptake value (SUVmean) 5.2 of the primary tumor before treatment, while after treatment these values were determined as 7.7- 4.4- 23.0- 2.5 and a significant decrease was observed in all parameters (p<0.001). In patients who achieved pathological complete response (PCR), a significant post-treatment decrease was observed in primary tumor MTV, SUVmax, SUVmean and TLG values, and this decrease was significantly greater compared to the non-PCR group (p<0.05). In addition, it was shown that the percentage changes in MTV, TLG and SUVmax iv parameters before and after treatment provided significant cut-off values in predicting PCR in the ROC curve analysis. In terms of clinical response, the reduction rates of MTV and TLG were significantly higher in the group with clinical response (p<0.05). In patients who received the FLOT chemotherapy regimen including 5-fluorouracil, calcium folinate, oxaliplatin and docetaxel, the reduction rates in primary tumor and total TLG were found to be statistically significantly higher compared to the group receiving FOLFOX including calcium folinate, 5-fluorouracil and oxaliplatin or XELOX including capecitabine and oxaliplatin (p<0.05). The percentage change rates of PET-CT parameters during the treatment process were examined according to the histological subtypes of the patients, and as a result of the analyses, no statistically significant difference was found between the histological type and the reduction rates of PET-CT parameters (p > 0.05). Conclusion: In this study, the relationship between changes in PET-CT parameters before and after treatment and pathological complete response (PCR) was investigated in patients with gastric cancer who received neoadjuvant chemotherapy. The findings demonstrated significant post-treatment reductions in metabolic parameters at the primary tumor level, particularly MTV, SUVmax, SUVmean, and TLG. The rates of decrease in these parameters were found to be markedly higher in the PCR group compared to the non-PCR group. In the evaluation performed using ROC analysis, these parameters were shown to have significant diagnostic value in predicting PCR. Furthermore, reductions in total MTV and TLG levels were also found to be significantly associated with PCR. In the analyses conducted according to clinical response, the reduction rates in MTV and TLG were determined to be higher in patients with clinical response. These results support that the reduction rates in PET CT parameters may serve as potential biomarkers in predicting both clinical and pathological response.