18 F-FDG PET/CT feature of pancreatic adenosquamous carcinoma with pathological correlation.

Purpose: To investigate ¹⁸ F-FDG PET/CT feature of pancreatic adenosquamous carcinoma (PASC) in contrast with conventional pancreatic ductal adenocarcinoma (PDAC), and its correlation with pathological findings.
Patients and Methods: Patients with PASC or PDAC confirmed by surgical pathology, who underwent FDG PET/CT scanning before surgical resection, were retrospectively studied. PASC group and conventional PDAC group included 13 and 104 patients, respectively. Delayed phase of PET/CT scanning was performed in 12 patients with PASC and 99 with PDAC. Maximum standardized value (SUVmax) was measured, and the mean retention index (RI) was calculated by ([PET _120min SUVmax]-[PET _60min SUVmax]) ÷ PET _60min SUVmax × 100%.
Results: On PET/CT, all lesions of PASC group showed intense FDG uptake, and the SUVmax were significantly higher than the lesions of conventional PDAC group both on the early [10.43 ± 5.10 (4.37-24.00) vs. 7.31 ± 3.86 (1.93-21.08), P = 0.011] and delayed phase [13.29 ± 6.04 (5.72-28.16) vs. 8.84 ± 5.14 (1.92-27.58), P = 0.005]. On the delayed phase, all lesions of PASC group had increased SUVmax with positive RI value (27.04% ± 8.87%, 7.14-39.27%). For conventional PDAC group, 81 lesions had increased SUVmax with positive RI value (27.25% ± 19.10%, 1.09-104.49%), while eighteen (18.18%) lesions of PDAC group had slightly decreased SUVmax, and their RI value were negative (- 11.35% ± 13.50%, - 43.17 to - 0.14%). The proliferative index (Ki-67) of lesions of PASC group was positively correlated with both the early (P = 0.034, r = 0.671) and delayed SUVmax (P = 0.019, r = 0.721). The RI value of lesions with adjacent organ invasion in PASC group was significantly higher than those without invasion (33.25% ± 4.92% vs. 20.83% ± 7.49%, P = 0.007).
Conclusion: PASC has more intense FDG uptake than conventional PDAC both on early and delayed phase. RI value of PASC was positive. Negative RI value may be helpful for differentiating PDAC from PASC. SUVmax and RI value may be helpful for prediction of its malignancy and invasion.