Gemcitabine With or Without Capecitabine and/or Radiation Therapy or Gemcitabine With or Without Erlotinib in Treating Patients With Locally Advanced Pancreatic Cancer That Cannot Be Removed by Surgery

OBJECTIVES: Primary * To assess whether administrating chemoradiotherapy in patients whose tumor is controlled after 4 months of induction chemotherapy (CT) increases survival compared with continuation of the same CT in patients with unresectable, locally advanced adenocarcinoma of the pancreas. Secondary * To assess whether erlotinib hydrochloride combined with gemcitabine hydrochloride and administered as maintenance treatment increases progression-free survival compared with gemcitabine hydrochloride alone and without maintenance treatment. * To evaluate the response rate in the CT and chemoradiotherapy (CRT) arms. * To evaluate tolerance to erlotinib hydrochloride as maintenance treatment after the end of CT or CRT. * To study the predictive molecular factors (i.e., survivin, K-ras, EGFR, PTEN, or AKT) of survival. OUTLINE: This is a multicenter study. Patients in the first randomization are stratified according to center and ECOG performance status (0-1 vs 2). Patients in the second randomization are stratified according to center and initial treatment arm (I vs II). * First randomization: Patients are randomized to 1 of 2 treatment arms. * Arm I: Patients receive gemcitabine hydrochloride IV over 30 minutes on days 1, 8, 15, 22, 29, 36, and 43. Following the first evaluation, patients continue to receive gemcitabine hydrochloride on days 57, 64, 71, 85, 92, and 99 for a total of 4 months. * Arm II: Patients receive gemcitabine hydrochloride IV over 30 minutes on days 1, 8, 15, 22, 29, 36, and 43. Following the first evaluation, patients continue to receive gemcitabine hydrochloride on days 57, 64, 71, 85, 92, and 99. Patients also receive oral erlotinib hydrochloride once daily for 4 months. After completion of treatment in the first randomization proceed to the second randomization. * Second randomization: Patients are randomized to 1 of 4 treatment arms. * Arm I: Patients continue gemcitabine hydrochloride as in arm I in the first randomization on days 113, 120, and 127 and on days 141, 148, and 155 for 2 months in the absence of disease progression. * Arm II: Patients continue gemcitabine hydrochloride as in arm II in the first randomization on days 113, 120, and 127 and on days 141, 148, and 155 and oral erlotinib hydrochloride daily for 2 months followed by erlotinib hydrochloride alone as maintenance therapy in the absence of disease progression. * Arm III: Patients receive oral capecitabine twice daily and undergo radiotherapy beginning on day 127, 5 days a week, for 6 weeks, in the absence of disease progression. * Arm IV: Patients receive oral capecitabine twice daily and undergo radiotherapy beginning on day 127, 5 days a week, for 6 weeks. Beginning 15 days after completion of CRT, patients receive a reintroduction of oral erlotinib hydrochloride alone once daily in the absence of disease progression or unacceptable toxicity. Tumor tissue will be analyzed for the relationship between biological markers and resistance to treatment. After completion of study treatment, patients are followed every 2 months.