[en] Purpose: CA 19-9 has been identified as a tumor marker for pancreatic carcinoma and has been shown to have some utility in predicting outcome in surgically treated patients. The purpose of this study was to evaluate its usefulness as a prognostic indicator in patients treated with radiotherapy. Materials and Methods: A retrospective review of all patients treated with radiotherapy of definitive intent (N=104) for carcinoma of the pancreas at Fox Chase Cancer Center from 1980-1994 was undertaken. Patients were categorized into four groups: planned preoperative radiation with resection (N=25), planned preoperative radiation without successful resection (N=35), postoperative radiation (N=21), and radiation without planned resection (N=23). For each group except those treated without planned resection, median dose for external beam radiotherapy was 50.4 Gy (range=21.6-63.0 Gy). Those in the fourth group were treated with a median dose of 55.8 Gy (range=36.0-60.4 Gy). Ninety-seven percent of patients in the first three groups were also treated with 5-FU based chemotherapy, as were 61% of those in the fourth group. Results: Mean/median survival for all groups was (14.6(10.0)) mos. (range=1-67 mos.). Univariate analysis showed significant differences in survival among the groups: preop with resection 22.2 mos., preop without resection 9.5 mos., postop 16.8 mos. and without planned resection 12.2 mos. (p=0.0005). Overall, patients who underwent resection had a mean survival of 19.7 mos., compared to 10.6 mos. in those who did not (p=0.0006). CA 19-9 level at diagnosis was found to be a significant prognostic indicator on univariate analysis, with a mean survival of 8.3 mos. in those having a level greater than the median of 680, compared to 20.2 mos. in those who did not (p=0.0003). Similarly, post-treatment nadir was significant, with a mean survival of 11.3 mos. in those with levels above the median of 162.5, versus 26.1 mos. in those below the median (p=0.001). On stepwise multivariate analysis, pre-treatment CA 19-9 level was found to be a significant predictor of survival (p=0.0014). Other potential indicators of outcome, including age, sex, KPS, prediagnosis weight loss, location of tumor, clinical TNM staging, size of lesion, vascular involvement on angiography, and sequence of radiation with respect to resection, were evaluated and were not found to be significant. Conclusion: CA 19-9 was demonstrated to be a useful prognostic indicator in patients treated with radiotherapy, while other more traditional indicators of outcome were of less utility