Study of Romiplostim for Chemotherapy-induced Thrombocytopenia in Adult Subjects With Gastrointestinal, Pancreatic, or Colorectal Cancer

Inclusion Criteria: * Subject has provided informed consent prior to initiation of any study specific activities/procedures or subject's legally acceptable representative has provided informed consent prior to any study-specific activities/procedures being initiated when the subject has any kind of condition that, in the opinion of the investigator, may compromise the ability of the subject to give written informed consent. * Males or females greater than or equal to 18 years of age at signing of the informed consent. * Histologically or cytologically confirmed diagnosis of gastrointestinal, pancreatic, or colorectal adenocarcinoma, defined as cancers of the esophagus (including esophagogastric junction \[EGJ\] cancer), stomach, pancreas, colon, or rectum. Tumor stage will not affect eligibility. * Subjects must be receiving 1 of the following regimens: An oxaliplatin-based chemotherapy regimen, containing 5 FU or capecitabine plus oxaliplatin (irinotecan may be added for FOLFIRINOX or FOLFOXIRI) on a 14- or 21 day schedule, respectively; OR, subjects must have chemotherapy-induced thrombocytopenia from a non-protocol chemotherapy regimen, planning to start treatment with one of the protocol chemotherapy regimens which has been delayed greater than or equal to one week due to chemotherapy-induced thrombocytopenia. Note: Use of these regimens are permitted with (1) anti angiogenic agents (such as bevacizumab) or (2) targeted therapy (such as anti epidermal growth factor receptor agents); * Subjects must have a local platelet count ≤ 85 x 10\^9/L on study day 1. * Subjects must be at least 14 days removed from the start of the chemotherapy cycle immediately prior to study day 1 if they received FOLFOX, FOLFIRINOX or FOLFOXIRI, and 21 days removed if they received CAPEOX. * Subjects must have at least 3 remaining planned cycles of chemotherapy at study enrollment. * Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2. Exclusion Criteria: Previous or Current Medical Conditions * Acute lymphoblastic leukemia. * Acute myeloid leukemia. * Any myeloid malignancy. * Myelodysplastic syndrome. Baseline bone marrow biopsy is not required to rule out MDS. However, if a bone marrow biopsy and cytogenetics were performed as part of diagnostic or staging work-up, these results will be collected to confirm. * Myeloproliferative disease. * Multiple myeloma. * Within 4 months prior to enrollment, any history of active congestive heart failure (New York Heart Association \[NYHA\] Class III to IV), symptomatic ischemia, uncontrolled arrhythmias, clinically significant electrocardiogram (ECG) abnormalities, screening ECG with corrected QT (QTc) interval of \> 470 msec, pericardial disease, or myocardial infarction. * Major surgery ≤ 28 days or minor surgery ≤ 3 days prior to enrollment. * New or uncontrolled venous thromboembolism or thrombotic events within 3 months prior to screening. To be eligible, subjects must have received at least 14 days of anticoagulation for a new thrombotic event and considered to be both stable and suitable for continued therapeutic anticoagulation during trial participation. * History of arterial thrombosis (eg, stroke or transient ischemic attack) within 6 months of screening. * Evidence of active infection within 2 weeks prior to first dose of study treatment. * Known human immunodeficiency virus infection. Subjects without a documented diagnosis in their medical history will require a local laboratory assessment at screening. If local laboratory results are not available, use central laboratory results. * Known active chronic hepatitis B or C infection. Subjects without a documented diagnosis in their medical history will require a local laboratory assessment at screening. If local laboratory results are not available, use central laboratory results. Hepatitis B and C infection is based on the following results: * Positive for hepatitis B surface antigen (HBsAg) (indicative of chronic hepatitis B or recent acute hepatitis B). * Negative HBsAg and positive for hepatitis B core antibody: hepatitis B virus DNA by polymerase chain reaction (PCR) is necessary. Detectable hepatitis B virus DNA suggests occult hepatitis B. * Positive Hepatitis C virus antibody (HCVAb): hepatitis C virus RNA by PCR is necessary. Detectable hepatitis C virus RNA suggests chronic hepatitis C. * Secondary malignancy within the past 5 years except: * Adequately treated non-melanoma skin cancer or lentigo maligna without evidence of disease. * Adequately treated cervical carcinoma in situ without evidence of disease. * Adequately treated breast ductal carcinoma in situ without evidence of disease. * Prostatic intraepithelial neoplasia without evidence of prostate cancer. * Adequately treated urothelial papillary noninvasive carcinoma or carcinoma in situ. * Malignancy treated with curative intent and with no known active disease present for at least 3 years before enrollment and felt to be at low risk for recurrence by the treating physician * Thrombocytopenia due to another etiology other than CIT (eg, chronic liver disease, prior history of immune thrombocytopenia purpura). Prior/Concomitant Therapy • Previous use of romiplostim, pegylated recombinant human megakaryocyte growth and development factor, eltrombopag, recombinant human TPO, any other TPO receptor agonist, or any investigational platelet producing agent. Prior/Concurrent Clinical Study Experience • Currently receiving treatment in another investigational device or drug study, or less than 28 days since ending treatment on another investigational device or drug study(ies). Other investigational procedures while participating in this study are excluded. Diagnostic Assessments * Anemia (hemoglobin \<80 g/L \[8 g/dL\]) on the day of initiation of investigational product as assessed by local labs. Use of red cell transfusions and erythropoietic stimulating agents is permitted throughout the study as per institutional guidelines. * Neutropenia (absolute neutrophil count 1 x 10\^9/L) on the day of initiation of investigational product as assessed by local labs. Use of granulocyte-colony stimulating factor is permitted throughout the study as per institutional guidelines. * Abnormal renal function with creatinine clearance \< 30 mL/min using the Cockcroft-Gault estimated creatinine clearance as assessed by local laboratory during screening. If local laboratory results are not available, use central laboratory results. * Abnormal liver function (total bilirubin \> 3 X ULN; alanine aminotransferase \[ALT\] or aspartate aminotransferase \[AST\] \> 3 X ULN for subjects without liver metastases or ≥ 5 X ULN for subjects with liver metastases) as assessed by local laboratory during screening. If local laboratory results are not available, use central laboratory results. Other Exclusions * Females who are pregnant or breastfeeding or planning to become pregnant or breastfeed during treatment and for an additional 6 months after treatment (and chemotherapy) discontinuation (females of childbearing potential should only be included after a confirmed menstrual period and a negative highly sensitive urine or serum pregnancy test.) * Females of childbearing potential unwilling to use a highly effective method of contraception during treatment and for an additional 6 months after treatment (and chemotherapy) discontinuation. * Males unwilling to use contraception\* (male condom or sexual abstinence) or their female partner(s) of childbearing potential who are unwilling to use a highly effective method of contraception during treatment (and chemotherapy) and for an additional 6 months after treatment (and chemotherapy) discontinuation. \*If the male's sole partner is of non-childbearing potential, he is not required to use additional forms of contraception during the study. * Subject has known sensitivity to any of the products to be administered during dosing. * Subject likely to not be available to complete all protocol-required study visits or procedures, and/or to comply with all required study procedures (eg, COAs) to the best of the subject and investigator's knowledge. * History or evidence of any other clinically significant disorder, condition or disease (with the exception of those outlined above) that, in the opinion of the investigator or Amgen physician, if consulted, would pose a risk to subject safety or interfere with the study evaluation, procedures or completion. * Male subjects with a pregnant partner who are unwilling to practice abstinence or use a condom during treatment (and chemotherapy) and for an additional period of 6 months after treatment (and chemotherapy) discontinuation. * Male subjects unwilling to abstain from donating sperm during treatment (and chemotherapy) and for an additional 6 months after treatment (and chemotherapy) discontinuation.