Abstract 4762: Clinicopathologic findings of borderline resectable pancreatic cancer after neoadjuvant chemoradiotherapy
Authors: Naito Yoshiki , Nakayama Masamichi , Ishikawa Hiroto , Takahashi Kenjiro , Hisaka Toru , Okuda Koji , Fukahori Masaru , Ishida Yusuke , Okabe Yoshinobu , Mihara Yutaro , Tanigawa Masahiko , Akiba Jun , Torimura Takuji , Yano Hirohisa 
Published: August 2018

BACKGROUND: The resection rate and survival period of resectable pancreatic ductal adenocarcinoma (PDAC) have increased gradually. Unfortunately, only 15-20% of patients have resectable disease at diagnosis, with the remainder presenting with distant metastatic or locally advanced tumors. Borderline resectable PDAC (BR-PDAC) is defined as a tumor that involves the portal vein (PV) and/or superior mesenteric vein (SMV), and has low resectability. However, there are many practical advantages to neoadjuvant chemoradiotherapy (NAC-RT) for BR-PDAC. Although the clinical effects of NAC-RT in BR-PDAC have been discussed, only a few studies have reported pathological features. We herein studied the effect of NAC-RT on the histological features of BR-PDAC.

MATERIALS AND METHODS: Tissue samples of 14 patients with BR-PDAC undergoing NAC-RT (NAC-RT group; male: 7 patients, female: 7 patients; average age:64.8+8.1 years) and 78 patients with conventional PDAC (control group), resected at the Kurume University Hospital were obtained. The BR-PDACs had PV and/or SMV invasion at initial clinical diagnosis. All patients with BR-PDAC underwent NAC-CRT, comprising chemotherapy and external beam irradiation (50.4 Gy). The microvessel invasion (MVI), lymphovascular invasion (LVI), neural invasion (NI), portal vein invasion (PVI), extrapancreatic plexus invasion (PLI), and TNM classification in the surgical specimens were examined. All statistical analyses were performed using StatMate IV (ATMS, Tokyo, Japan). All statistical tests were two-tailed, and P &lt; 0.05 was considered statistically significant.

RESULTS: The distribution of stages in the NAC-RT group was as follows: stage IA (n = 5, 36%), IIA (n = 6, 43%), IIB (n = 3, 21%). The pathological grade was determined to be G1 in 9 cases (64%), G2 in 4 cases (28%) and G3 in 1 case (8%). The difference in average tumor size between the NAC-RT and control groups was significant (P&gt; 0.001). Lymph node metastases were significantly infrequently observed in the NAC-RT group compared with the control (P=0.009). The NAC-RT group had a significant lower MVI (29%, 4/14) and LVI (57%, 8/14) than the control group (MVI: P&lt;0.001, LVI: P=0.011). However, there was no significant difference in NI (P=0.129). Ten patients without PVI and /or PLI in the NAC-RT group (71%) had significantly better prognosis than those in the control group (P=0.029), although there was no significant difference in overall survival rates between both groups (P=0.100).

CONCLUSIONS: NAC-RT might be more advantageous by inhibiting local invasion, hematogenous and lymphatic metastasis, and could contribute to a better prognosis in patients with BR-PDAC, partly due to the prevention of PVI and/or PLI in pancreatic cancer.

Citation Format: Yoshiki Naito, Masamichi Nakayama, Hiroto Ishikawa, Kenjiro Takahashi, Toru Hisaka, Koji Okuda, Masaru Fukahori, Yusuke Ishida, Yoshinobu Okabe, Yutaro Mihara, Masahiko Tanigawa, Jun Akiba, Takuji Torimura, Hirohisa Yano. Clinicopathologic findings of borderline resectable pancreatic cancer after neoadjuvant chemoradiotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4762.