Recent developments in pancreatic cancer imaging, are rapidly changing the field [8]. The main concern of this study was to evaluate, if the nonfunctioning PNETS could be detected with 18F-FDG PET/CT.
FDG is a glucose analog that accumulate in the tumor cells proportionally to their glucose metabolic activity, allowing cell to be detected by 18F-FDG PET/CT images [9].
In the present study we found that 86.7% of nonfunctioning PNETS can be detected by 18F-FDG PET/CT, 26 of 30 patients have SUVmax above 2.5 while 4 patients were below 2.5.
This was in concordant with Luo et al. [10] who revealed that 90.3%of nonfunctioning PNETS can be visualized by PET/CT, suggesting that 18F-FDG PET/CT can be used to detect nonfunctioning PNETS.
Many published researches [11, 12] reported that tumors with increase FDG accumulation seem more aggressive and correspond to bad prognosis as the majority of nonfunctioning PNETS are undifferentiated with high proliferative activity.
In the present study we analyze the effect of the tumor size, grade, and the TNM stage of the lesion on the FDG uptake of PET/CT.
Our results show positive correlation between the tumor size and the tumor uptake of FDG, as tumors with avid FDG were larger in size than the poorly avid one.
These agree with Partelli et al. [13] who concluded that the uptake of FDG in NF PNETs was significantly related with tumor size.
Further in our study we found significantly associated correlation between tumor grade and the FDG uptake of the tumor and this correlation maintained significant with the rate of tumor proliferation (p = 0.554). Our results show that 10.7% of patients were Grade 1, 57% were Grade 2 and 25% were Grade 3. In addition, we also examined the TNM stage, which was found to be significantly associated with the FDG uptake (p = 0.021).
Majala et al. [14] prospectively investigated well differentiated metastatic NETs and reported that FDG is positively correlated with decreased progression and overall survival. They found 20% of Grade 1 were PET/CT positive compared with 76% of Grade 2.
Our results show that increased FDG uptake is significantly associated with poorly differentiated tumor nature. 4 of stage I patients show SUV max below 2.5 while 26 patients have SUV max more than 2.5, as follows Grade 1 tumor manifested in 3 cases, Grade 2 in 16 cases and Grade 3 in 7 cases.
Diletta et al. [15] and Asagi et al. [16], found that the significance of 18F-FDG PET/CT altered the treatment plan of the nonfunctioning PNETS patients as it detects 90.5% of distant metastasis, suggesting that it can be utilized to stage non-functioning PNETs.
The results of our study show, that the 18F-FDG PET/CT enables the detection of aggressive tumors with avid SUVmax more than 2.5 among the well differentiated NF-PNETs. Thus it could supplement the evaluation of the tumor nature and tailor more appropriate management decisions, however false negative imaging findings should be considered. In addition, involvement of 18F-FDG PET/CT in clinical management of NF PNETs was found to restage the primary tumor.
This agree with our results as we found that of 30 patients, 4 patients of well differentiated tumor had altered their clinical strategies according to the results of PET/CT examinations.
18F-FDG PET/CT upstaged 1 patient with stage IB and 3 patients with IIA and B to stage IV (Fig. 1, 2, 3).
Limitations
We encountered some limitations in this study as small sample size of patients with non-functioning PNETs. Most patients present in late stage of this disease.