This study demonstrates the significance of PET/CT uses during the evaluation of cases with non-small cell bronchogenic carcinoma, either during staging or during follow-up to assess the therapeutic response. PET/CT showed a change in the TNM staging in 40% of the studied cases and a change in follow-up response in 30% of the studied cases. Eight cases in group T representing 26.7% and seven cases in group F representing 23.3% showed a change in the management strategy, according to the change in their surgical staging and the change in their treatment response evaluation, respectively.
This is explained by the difference between the two modalities as the CT gives us information about the morphology of the tumor and the morphology of the associated metastatic lesions as well as anatomical details while the PET/CT has the ability to combine both the morphological and the functional activity with the advantage of detection of the functional changes of both the tumoral mass and the associated metastatic lesions.
A lot of researchers studied the impact of PET/CT in bronchogenic carcinoma staging [14,15,16,17,18,19,20,21,22,23]. We used the eight TNM staging system which was already established since early 2017 in controversy to most of the studies used the older seventh edition of TNM staging as in a study done by Chao and Zhang [11].
Twelve cases out of 30 cases in group T representing 40% of cases showed a change in the TNM staging by PET/CT compared to CT alone, and this is almost close to the results found by Bury et al., Hicks et al., Taus et al., and Zheng et al. who concluded that 34%, 43%, 35%, and 35% of their cases showed change in their TNM staging when assessed by PET/CT [15, 18, 22, 23]. In controversy, Pieterman et al. found 62% of cases with a change in their TNM staging which is higher than our result [17] while Takeuchi et al. found the change in TNM staging in 28.7% of their cases [21].
In our study, out of the 12 cases in group T with a change in TNM staging, we found 8 cases representing 26.7% with the change in the TNM staging affected the surgical staging with subsequent changes in treatment strategy. The rest 4 cases showed no change in the surgical staging with no effect on the treatment plan. This is close to the result found by Bury et al. and Hicks et al. who found PET/CT impact on the management of 25% and 35% of their cases [15, 18].
The explanation of the TNM staging difference found between PET/CT compared to CT is summarized in Fig. 7 which highlights the effect of PET/CT in the precise and accurate delineation of the tumoral mass separating it from the surrounding nonmalignant pulmonary reaction, especially in T2 stage, and this is consistent with Chao and Zhang and Steinert [11, 24]. Aydin et al. stated that PET/CT measurements of the tumor size were more compatible with the histopathological size compared to CT, and this will affect the T staging which depends on the tumoral size [25]. Also, Hochhegger et al. studied the ability of PET/CT to differentiate the tumor and post-obstructive pulmonary changes which is considered challenging with T staging [26].
Four cases of our study showed changing in their TNM staging due to the difference in diagnosis of the nature of pulmonary nodules. The ability of PET/CT to differentiate the benign from the malignant nodules affects both T and M staging, and this is consistent with Volpi et al. who discussed the accuracy of PET/CT in differentiating the benign nodules from a malignant one [6].
PET/CT is a known modality to detect the malignant activity in the mediastinal lymph nodes more accurately compared to the CT which depends only on the nodal size with the accuracy reaching to about 90% in the diagnosis of malignant mediastinal lymphadenopathy [6, 11, 27].
CT depends only on the size of the lymph node during N staging. However, this carries a lot of fallacies as in post obstructive pneumonitis causing false-positive enlargement of the lymph nodes and also, normal-sized lymph nodes may be found to be metastatic on histopathological verification [28, 29]. Valopi et al. stated that patients with negative mediastinal lymph nodes on PET/CT can proceed to their management, according to the rest of T and M staging while the patients with positive nodal lesions may need further assessment via biopsy using mediastinoscopy for accurate histopathological verification avoiding false-positive results [7].
PET/CT is a known modality to detect the hidden bone marrow infiltrates being more accurate than CT and even bone scan to detect bony metastases, which are a common site for metastases in cases with bronchogenic carcinoma [6, 11, 27, 30]. Ten percent of patients with bronchogenic carcinoma found to have positive distant metastases by PET/CT not detected by CT alone [27].
On follow-up patients after starting their therapy (group F), we found nine cases (30%) with a change in therapeutic response assessment comparing the PERCIST criteria obtained by PET/CT and RECIST criteria obtained by CT alone, and this affects the treatment strategy and plan for seven cases (23.3%).
Multiple research papers are published studying the impact of PET/CT in the evaluation of the treatment response in cases with non-small cell lung cancer [31,32,33].
Although CT is the modality of choice on follow-up cases of lung cancer to evaluate the therapeutic response with RECIST criteria which is widely accepted and used for assessment, yet it still depends on the tumoral size change which shows some sort of variability between observers especially in irregular and speculated lesions. Also, CT cannot detect the activity changes occurred in response to therapy [34].
William et al. found a discrepancy between the CT RECIST and the histopathological results among 41% of the studied cases during follow-up after neoadjuvant chemotherapy [35] which was close to our results. However, in our study, we compared the result of the PET/CT to the CT alone, in controversy to William et al. who compared the PET/CT with the histopathology.
Our results were close to the result of Jimenez-Bonilla et al. and Marcus et al. who found that PET/CT resulted in a change in management between 30.19% and 28.1% of their patients, respectively, who did PET/CT to evaluate the therapeutic response [36, 37]. This was in controversy to Hicks et al. and You et al. who found a change in the management and therapeutic plane between 63.5% and 57% of their patients, respectively, when using PET/CT in the evaluation of therapeutic response [18, 38].
The main limitation of our study was the small sample size due to the high cost of the technique. A multi-centric study will be needed to obtain more accurate results when applied to a larger number of patients.