Inclusion Criteria:
* Age ≥ 18 years
* Eastern Cooperative Oncology Group (ECOG) performance score 0 or 1
* Starting platinum-based doublet/triplet therapy for gynecologic or gastrointestinal cancer in the non-curative setting, with at least 16 weeks of chemotherapy and/or immunotherapy planned prior to registration; able to start study treatment ≤ 7 days prior to starting chemotherapy
* Life expectancy at least 6 months
* Hemoglobin ≥ 10 g/dL (obtained ≤ 30 days prior to registration)
* Creatinine ≤ 1.5 x upper normal limit (UNL) OR calculated creatinine clearance ≥ 50 ml/min using the Cockcroft-Gault (obtained ≤ 30 days prior to registration)
* Alanine aminotransferase (ALT) and aspartate transaminase (AST) ≤ 1.5 x UNL; \[≤ 5 x upper limit of normal (ULN) for patients with liver involvement\] (obtained ≤ 30 days prior to registration)
* Ability to complete patient questionnaires alone or with assistance and to be willing to be contacted by study staff
* Provide written informed consent
* Negative pregnancy test done ≤ 7 days prior to registration, for persons of childbearing potential only NOTE: If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required
* Willing to use a highly effective method of contraception from the first dose of study medication through 30 days after the last dose of study medication, for persons of childbearing potential or persons able to father a child only
* Willing to return to enrolling institution for follow-up (during the Active Monitoring Phase of the study)
Exclusion Criteria:
* Known hypersensitivity to fucoidan or seaweed products
* Currently using any other pharmacologic agents to specifically treat fatigue including psychostimulants or antidepressants. Note: Antidepressants used to treat items other than fatigue (such as hot flashes or depression) are allowed if the patient has been on a stable dose for ≥ 1 month prior to registration and plans to continue such for 8 weeks. Exercise is allowed
* Psychiatric disorder such as untreated/uncontrolled depression, manic depressive disorder, obsessive compulsive disorder or schizophrenia (defined per medical history)
* Surgery that required general anesthetic ≤ 4 weeks prior to registration
* Malnutrition, active infection, severe depression, significant pulmonary disease, and/or cardiovascular disease that the attending physician feels could be causing the patient's fatigue
* Use of any over-the-counter herbal/dietary supplement marketed for fatigue or energy (for example, products containing ginseng, rhodiola rosea, guarana, or anything called an "adaptogen"), including current use of fucoidan
* Current use of warfarin, heparin, enoxaparin, or a novel anticoagulant or known bleeding disorder/abnormal prothrombin time (PT)/partial thromboplastin time (PTT) at baseline
* Current use of bevacizumab
* Untreated thyroid conditions
* Use of chemotherapy and/or immunotherapy ≤ 90 days prior to registration
* Unwillingness to follow study related procedures
* Inability to provide informed consent
