• Fatigue Interference subscale of Fatigue Symptom Inventory [ Time Frame: 2 weeks post-intervention ]
  Seven items are rated on 11-point scales (0=no interference to 10=extreme interference) that assess the extent to which fatigue in the past week interfered with general level of activity, ability to bathe and dress, normal work activity (including housework), ability to concentrate, relations with others, enjoyment of life, and mood. Higher scores indicate greater fatigue interference. This is the primary outcome for patients.
• Short-form of Zarit Burden Interview [ Time Frame: 2 weeks post-intervention ]
  Twelve items are rated on 5-point scales (0=never to 4=nearly always) that assess personal strain and role strain due to caregiving. Higher scores indicate greater caregiving burden. This is the primary outcome for caregivers.

• PROMIS Sleep-Related Impairment [ Time Frame: 2 weeks post-intervention ]
  This 8-item measure assesses the perceived interference of sleep problems with activities, mood, and cognition (e.g., difficulty concentrating or completing tasks). Each item is rated on a scale from 1 (not at all) to 5 (very much) with higher scores indicating greater sleep-related impairment. This is a secondary outcome for patients.
• PROMIS Ability to Participate in Social Roles and Activities [ Time Frame: 2 weeks post-intervention ]
  This 6-item measure assesses participants' ability to participate in social roles and activities. The items measure difficulty engaging in social and recreational activities as well as usual work (including housework). Each item is rated on a scale from 1 (never) to 5 (always) and is reverse coded such that a higher score indicates greater ability to participate in activities. This is a secondary outcome for both patients and caregivers.
• Acceptance and Action Questionnaire-II [ Time Frame: 2 weeks post-intervention ]
  This 7-item measure assesses psychological flexibility, or the ability to fully experience the present moment while persisting in actions aligned with personal values. Each item is rated on a scale from 1 (never true) to 7 (always true). Higher scores indicate greater levels of psychological inflexibility. This is a secondary outcome for both patients and caregivers.
• McGill Quality of Life Questionnaire-Revised [ Time Frame: 2 weeks post-intervention ]
  This 15-item measure evaluates physical, existential, and social well-being in patients with serious illnesses. Items are rated on 0 to 10 scales. This is a secondary outcome measure for patients.
• PROMIS Global Health [ Time Frame: 2 weeks post-intervention ]
  This 10-item measure assesses global health, including physical, mental, and social well-being. With the exception of pain, which is rated on a 0 to 10 scale, all items are rated on 5-point scales. This is a secondary outcome measure for caregivers.

• Behavioral: Acceptance and Commitment Therapy
  Across six weekly 50-minute sessions, advanced GI cancer patients and caregivers will practice various mindfulness exercises, clarify their values, and set specific goals in alignment with their values. Through in-session and home practice of skills, participants will learn new and more adaptive ways to respond to unwanted internal experiences (e.g., fatigue, distress). Participants will receive handouts on session topics and a CD that we developed to guide mindfulness practices.
• Behavioral: Education/Support
  Across six weekly 50-minute sessions, advanced GI cancer patients and caregivers will be directed to resources for practical and health information and contact information for psychosocial services. Sessions will include an orientation to the patient's medical center and treatment team, education regarding common quality-of-life concerns experienced by cancer patients and caregivers, and an overview of medical center and community resources for addressing these concerns. The therapist will also describe resources for addressing financial concerns and methods of evaluating health information available via the Internet and other modalities. Participants will receive handouts summarizing session topics and will be asked to review them as homework.

• Experimental: Acceptance and Commitment Therapy
  Patients and caregivers in the ACT arm will learn new and more adaptive ways to respond to difficult internal experiences (e.g., fatigue, thoughts, and feelings).
  Intervention: Behavioral: Acceptance and Commitment Therapy
• Active Comparator: Education/Support
  Patients and caregivers in the education/support arm will discuss their cancer-related concerns and receive education on services available in their medical center and community.
  Intervention: Behavioral: Education/Support

Patient Inclusion Criteria:

• Patient is at least 3 weeks post-diagnosis of stage IV gastrointestinal cancer (i.e., anal, colon, esophageal, gallbladder, liver, pancreatic, rectal, small intestine, or stomach cancer) and is receiving care at the Indiana University Simon Cancer Center or Eskenazi Health.
• Patient is at least 18 years of age.
• Patient can speak and read English.
• Patient has an eligible, consenting family caregiver (see criteria below).
• Patient has moderate to severe fatigue interference with functioning.

Patient Exclusion Criteria:

• Patient shows significant psychiatric or cognitive impairment that would preclude providing informed consent and study participation.
• Patient reports being able to do little activity on a functional status measure.
• Patient is receiving hospice care at screening.
• Patient does not have working phone service.
• Patient has hearing impairment that precludes participation.

Caregiver Inclusion Criteria:

• Family caregiver identified by a stage IV gastrointestinal cancer patient who meets the eligibility criteria.
• Caregiver has significant caregiving burden or distress
• Caregiver lives with the patient or has visited the patient in-person at least twice a week for the past month.
• Caregiver is at least 18 years of age.
• Caregiver can speak and read English.

Caregiver Exclusion Criteria:

• Caregiver shows significant psychiatric or cognitive impairment that would preclude providing informed consent and study participation.
• Caregiver does not have working phone service.
• Caregiver has hearing impairment that precludes participation.
• Patient declines study participation.