Gemcitabine Hydrochloride With or Without Erlotinib Hydrochloride Followed by the Same Chemotherapy Regimen With or Without Radiation Therapy and Capecitabine or Fluorouracil in Treating Patients With Pancreatic Cancer That Has Been Removed by Surgery

Inclusion Criteria

• Histologic proof of primary head of pancreas invasive adenocarcinoma managed with a potentially curative resection (i.e., removal of all gross tumor) involving a classic pancreaticoduodenectomy (Whipple) or a pylorus preserving pancreaticoduodenectomy; patients with invasive adenocarcinoma that also contains a component of intraductal papillary mucinous neoplasm (IPMN) are eligible
• The operating surgeon must document in the operative note that a complete gross excision of the primary tumor was achieved; the pathology report must include documentation of the margin status and the size of the tumor; the pathology report must also include the status of the three major margins-bile duct, pancreatic parenchyma, and retroperitoneal (uncinate)
• For patients who have not started their chemotherapy prior to registration, the interval between definitive tumor-related surgery and 1st step registration must be between 21-70 days; for patients entering on the study who have already received up to 3 months of adjuvant chemotherapy as per the treating institution, the interval between definitive tumor-related surgery and day one of adjuvant chemotherapy must be between 21-77 days
• Patients will be staged according to the 6th edition American Joint Committee on Cancer (AJCC) staging system with pathologic stage T1-3, N0-1, M-0 being eligible. Pathologic reporting using the College of American Pathologists (CAPS) format is strongly encouraged
• Age >= 18
• Zubrod performance status 0 or 1
• Complete history and physical examination including weight and Zubrod status within 31 days of study entry (or within 31 days prior to day 1 of chemotherapy post-surgery for those patients having started chemotherapy prior to first step registration)
• Before starting therapy the patient should be able to maintain adequate oral nutrition of >= 1500 calories estimated caloric intake per day and be free of significant nausea and vomiting
• Complete blood count (CBC)/differential obtained within 21 days of registration on study (or within 21 days prior to day 1 of chemotherapy post-surgery for those patients having started chemotherapy prior to first step registration)
• Absolute neutrophil count (ANC) >= 1,500/mm^3
• Platelets >= 100,000/mm^3
• Hemoglobin >= 8.0 g/dL (Note: The use of transfusion or other intervention to achieve hemoglobin [Hgb] >= 8.0 g/dl is acceptable)
• Post resection serum cancer antigen (CA)19-9 = 499/cu mm and their viral load is < 50 copies/ml; use of highly active antiretroviral treatment (HAART) is allowed

Exclusion Criteria

• Patients with non-adenocarcinomas, adenosquamous carcinomas, islet cell (neuroendocrine) tumors, cystadenomas, cystadenocarcinomas, carcinoid tumors, duodenal carcinomas, distal bile duct, and ampullary carcinomas; patients with tumors that are largely intraductal papillary mucinous neoplasms (IPMN) with a minimal or minor component of invasive carcinoma are not eligible; patients with acinar carcinomas are not eligible; patients with IPMN's that contain some secondary (minor) foci of adenocarcinoma are also not eligible
• Patients managed with a total pancreatectomy, a distal pancreatectomy, or central pancreatectomy
• Patients entering on the study after pancreaticoduodenectomy, who have not already started chemotherapy must not have had prior systemic chemotherapy for pancreas cancer; note that prior chemotherapy for a different cancer is allowable; for patients entering on the study who have already received up to 3 months of adjuvant chemotherapy as per the treating institution, patients must not have received adjuvant chemotherapy with agents other than gemcitabine, nab-paclitaxel, oxaliplatin, fluoropyrimidine, or irinotecan for the current pancreatic cancer; prior chemotherapy for a different cancer is allowable
• Prior radiotherapy to the region of the study cancer that would result in overlap of radiation therapy fields
• Previous history of invasive malignancy (except