Patients undergo tissue sample collection periodically for correlative studies. Samples are analyzed for thymidylate synthase (TS), ribonucleotide reductase (RR), excision-repair-cross-complementing (ERCC)-1 protein, deoxycytidine kinase mRNA. Biopsy tissues are also analyzed for gemcitabine triphosphate, dATP, and dCTP content. p53 status is assessed via immunohistochemistry and mRNA levels via quantitative polymerase chain reaction (PCR).