The aim of the current study was to elucidate the role of PET/CT in assessment of treatment response of patients with bronchogenic carcinoma.
Several studies highlighted the effectiveness of 18F-FDG-PET/CT in the post-treatment assessment and follow-up of lung cancer patients.
This study enrolled 20 patients (18 males and 2 females). Their ages ranged from 33 to 79 years with a median of 58 years, an IQR of 50–66.5 years, and a mean (± standard deviation) of 56.4 years (± 12.6 years). The number of males was significantly higher than the number of females in this study. In the current study, histopathological analysis of the lung tumors revealed the presence of 13 (65%) adenocarcinomas, 2 (10%) squamous cell carcinomas, and 5 (25%) small cell lung cancers. Sixteen (80%) and 4 (20%) tumors were located in the right and left lungs respectively. No significant difference was seen between the number of smokers (13, 67.5%) and non-smokers (7, 35%) in this study (x2 = 1.8, P = 0.18); however, a significant association between smoking and gender was noted (x2 = 3.92, P = 0.05) where a significantly larger number of smokers in this study were males.
In agreement with this study, Akl et al. included 404 confirmed cases of bronchogenic carcinoma to assess the clinicopathological profile of the bronchogenic carcinoma cases. They reported that male to female ratio was 4.6:1. The highest incidence was in the sixth and seventh decades of life (63.6%). Smoking was found to be the main risk factor in 75.7% of patients. Four types of bronchogenic carcinoma were found: squamous cell carcinoma 37.4%, adenocarcinoma 29.5%, small cell carcinoma 14.9%, large cell carcinoma 7.2%, and undifferentiated carcinoma 11.1% .
Regarding TNM staging, in this study, we used the new 8th TNM classification staging system in controversy to most of the studies which used the older 7th edition of TNM staging as in a study done by Chao and Zhang .
Many studies have reported the effect of PET/CT in the accurate T staging and tumor delineation from surrounding pulmonary reactions, and this is consistent with Chao and Zhang, Steinert, Aydin et al., and Hochhegger et al. who concluded that PET/CT measurements are more accurate and compatible with histopathological size when compared to CT, and this will affect T staging of the tumor [17,18,19,20].
In this study, we found out that comparison of the pre- and post-treatment SUV in the responder and non-responder groups revealed that the post-treatment SUV was significantly lower than the baseline SUV in the responder group (P = 0.008) while no significant difference existed between post-treatment and baseline values in the non-responder group, and this is almost close to the results found by Bahce et al. and Yamamoto et al. who studied the ability of post-therapeutic tumor SUV uptake to predict pathological response in patients with NSCLC and compared the results with the histopathology. They found a significant difference in the SUVmax on pre- and post-treatment FDG PET scans of patients who responded to treatment versus the scans of patients who did not have a response [21, 22].
In this study, we reported that when responder and non-responder groups were compared, no significant difference was found between the pre-treatment SUV of both groups (P = 0.396); however, the responder post-treatment SUV and ∆SUV were significantly lower than the non-responder values. This was in concordance with Huang et al. who investigated the role of SUVmax to predict the short-term outcome of chemo-radiotherapy in patients with advanced NSCLC and concluded that changes in SUVmax values were significantly lower in responders than in non-responders according to RECIST criteria which was used as a gold standard. The sensitivity, specificity, and accuracy of SUVmax change for predicting tumor response were 83.3, 84.6, and 84.9% respectively .
This agrees with Cerfolio et al. who studied the change of SUV to assess the effectiveness of chemo-radiotherapy in patients with NSCLC based on histopathological analysis, and reported that reduction in the ∆SUVmax of more than 80% can significantly predict a complete pathological response with a sensitivity of 90%, specificity of 100%, and accuracy of 96%. Also, Lee et al. concluded that single PET/CT scan taken after one cycle of treatment could predict pathological response and can be used as a measure to avoid ineffective treatment. They stated that a reduction of SUVmax by more than 20% was used as a criterion for a partial metabolic response (PMR) and an increase of SUVmax by more than 25% as criterion for progressive metabolic disease (PMD). Metabolic response was compared with conventional radiographic response according to WHO criteria [24, 25].
In addition to a study by Eschmann et al. who evaluated FDG-PET for assessment of therapeutic response and for prediction of patient outcome after radio-chemotherapy of patients with NSCLC, PET findings were compared with the histology of tumor samples. That study demonstrated that the sensitivity, specificity, and accuracy of SUVmax were 95, 80, and 91%, respectively .
In this study, assessment of therapy response using CT established by using RECIST 1.1 criteria, as radiologic assessment of size change and reduction of tumoral mass, thus proves as an extremely useful surrogate marker for quick assessment of tumor response to treatment and is now one of the methods of assessment of choice in most clinical trials to assess drug efficacy . In this study, we revealed that the strongest correlation was demonstrated between ∆SUV and ∆ size (r = 0.91, P<0.0001). This agrees with Fattah et al., Cappabianca et al., Lu et al., and Khalaf et al. who reported that the tumor size and the entity of necrosis are some of the factors that affect the SUVmax of a tumor with positive correlation between tumor diameter and SUVmax [28,29,30,31].
This study is almost close to the result found by Weber et al. who studied the use of FDG-PET/CT to predict response to chemotherapy in patients with advanced NSCLC and found close correlation between metabolic response and best response to therapy according to RECIST criteria (P < .0001; sensitivity and specificity for prediction of best response, 95% and 74%, respectively) .
In controversy, Sheikhbahaei et al. reported that although CT is the modality of choice on post-therapeutic assessment of lung cancer using RECIST criteria which is widely accepted and used for assessment, yet in case of irregular and spiculated lesions, it shows variable results due to variable observer views in size measurement. In addition, activity changes which occur after treatment cannot be detected by CT. Another limitation is the inability of CT to differentiate viable tumor accurately from post-therapeutic inflammation and fibrosis, or even benign changes such as consolidation .
It is also concordant with the study by Hicks et al. who reported that using CT in monitoring the rapidly growing tumors undergoing central necrosis, size change might not be detected, while PET/CT metabolic parameters that integrate both uptake intensity and tumoral volume are very helpful in follow-up of the necrotic tumors, post-therapeutic changes, or tumors associated with distal atelectasis .
Additionally, William et al. and Cerfolio et al. found a mismatch between the CT RECIST and the histopathological results among the studied cases during follow-up after chemotherapy. They stated that CT RECIST may have a limited role in histopathologic response assessment and prediction of survival in patients with NSCLC. Also, Erasmus et al. concluded that RECIST tend to misclassify tumor progression in 30% of lesions in their study [24, 34, 35].
This is consistent with Mac Manus et al. who studied the value of FDG PET and enhanced CT in NSCLC patients before and after chemo-radiotherapy and found poor agreement between metabolic PET and morphologic CT response categories which were identical in only 40% of the studied cases .
The limitations of the current study were that PET-CT is relatively more expensive than other scanning modalities, and this must be considered in the current financial climate; another limitation was the small sample size. Further studies with large patient numbers are needed to validate the results of our study.