Background: Pancreatic ductal adenocarcinoma (PDAC) is a lethal neoplasm that spreads to surrounding tissue or distant sites. This study investigated distant metastases in PDAC patients with or without preoperative chemoradiation therapy (CRT), focusing on vitamin D levels and bone density. Methods: This study included 146 patients with PDAC who underwent surgery from 2007 to 2014. Bone density was evaluated using computed tomography, and the preoperative vitamin D level was calculated by enzyme-linked immunosorbent assay (ELISA) for patients with available plasma (48 cases). Results: When the patients were divided into two groups according to the change in bone density, the group with decreased bone density had a shorter distant metastasis-free survival time (DMFS) after surgery than the other group (p < 0.05). Low vitamin D was a weak predictor of DMFS, but the difference was not significant (p = 0.08), perhaps because of the sample size. Multivariate analysis indicated three significant factors associated with distant metastasis: a decrease in bone density (hazard ratio [HR], 2.17; p = 0.04), normalization of the Dupan-2 value after surgery (hazard ratio [HR], 0.39; p = 0.02), and completion of adjuvant chemotherapy (HR, 0.29; p < 0.01). Univariate analysis showed that a low vitamin D concentration (<20 pg/ml) was a risk factor (p = 0.04) for bone density change. Multivariate analysis found that preoperative CRT was the only factor associated (±, OR, 5.8; p = 0.04) with bone density change, suggesting that preoperative CRT significantly decreases bone density in patients with insufficient vitamin D. Conclusion: Patients treated with preoperative CRT tend to have impaired bone density, which is a predictor of distant metastasis. Thus, vitamin D supplementation may decrease distant metastasis.
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