Participants' use of the mobile application will be assessed using a measure developed specific to components of the proposed mobile application. Participants will be asked about how frequently they have used components of the mobile application outside of session since the previous session or last assessment depending on the timing of the questionnaire. A scale ranging from 0 "not at all" to 5 "2 or more times a day" will be used.

Symptoms of Anxiety will be assessed using the Patient Reported Outcomes Measurement Information System Anxiety Short Form-8a, an 8-item measure assessing symptoms of anxiety in the last week. Participants are asked to respond to items (e.g., "I felt nervous," "I felt tense") using a five-point scale ranging from 1 "never" to 5 "always". Total scores are then converted to T-scores. Items are summed and converted to standardized t-scores with a mean of 50 and standard deviation of 10. Higher T-scores indicate higher levels of anxiety. T-scores of 55 to 60 indicate mild levels of anxiety, 60 to 70 indicates moderate levels of anxiety, and greater than 70 indicate severe levels of anxiety.

Symptom interference will be assessed using the Illness Intrusiveness Rating Scale (IIRS). The IIRS assesses the extent to which an illness and/ or its treatments interfere with 13 quality of life domains (e.g., health, diet, work, sex life, active recreation). Items are rated on a 7-point scale from 1 "not very much" to 7 "very much." The total score ranges from 7 to 91, where a higher score indicates greater interference.

The Brief Pain Inventory is a 9-item, self-report measure assessing pain severity and interference from pain across important life domains (e.g., general activity, work, relations with others). Participants rate their pain on a scale from 0 "no pain" to 10 "pain as bad as you can imagine." Pain severity is calculated as the average of four items assessing participants' worst, least, current, and average (in the last week) pain on a scale from 0 "no pain" to 10 "worst pain." Pain interference is computed as the average of seven items, which ask about the interference of pain across different life domains (e.g., general activity, mood, relations with other people).

Fatigue will be assessed using the Patient Reported Outcomes Measurement Information System Fatigue Scale, a 6-item self-report measure of fatigue. Participants are asked to think about the last week when responding to each item (e.g., "In the past 7 days, how run-down did you feel, on average?"). Items are summed and converted to standardized t-scores with a mean of 50 and standard deviation of 10. A higher score indicates greater fatigue. T-scores of 55 to 60 indicate mild levels of fatigue, 60 to 70 indicates moderate levels of fatigue, and greater than 70 indicate severe levels of fatigue.

The Stanford LCAT is a categorical item that assesses the type of physical activities participants do.

The FACIT assesses the spiritual wellbeing of participants with 12-item questionnaire on a scale from 0 = "not at all" to 4 = "very much."

The AAQ is a 7-item questionnaire to track psychological flexibility related to coping with cancer and cancer treatment. The scale ranges from 1 = "never true" to 7 "always true." Item is scored by adding all of the responses together.

The VQ is a 10-item self-report questionnaire with a scale 0 = "not true at all" to 6 "completely true."

The 17-item Group Therapy Experiences Scale will be used to assess the level of cohesion among group members (e.g., development of positive relationships, comfort level with other group members). Items 1-16 are rated on a 5-point scale with 1 = "strongly agree" to 5 = "strongly disagree." Item 17 is an open-ended question, "was there something in the group today that helped or hindered you?"relationships, comfort level with other group members). Items are rated on a 4-point scale with 1= "strongly disagree" to 4= "strongly agree."

The PROMIS Social Isolation Scale is a 6-item measure is used to assess social isolation. Participants are asked to rate each item (e.g., "I felt left out," "I feel that people avoid talking to me") on a scale from 1= "never" to 5= "always."

The Self-Efficacy for Managing Chronic Disease Scale is a 6-item scale. Participants rate their confidence in keeping pain, fatigue, emotional distress, and other symptoms from interfering with things they want to do on a scale from 1 "not at all confident" to 10 "totally confident."

The PROMIS Self-Efficacy for Managing Chronic Conditions - Managing Symptoms - Short Form 4a is a 4-item scale. Participants rate their confidence in managing their symptoms during daily activities, with relationships with friends and family, in a public place, and working with their doctor to manage these symptoms on a scale from 1 = "I am not at all confident" to 5 "I am very confident."

The PROMIS Emotional Support Short Form is a 6-item measure used to assess emotional support. Participants are asked to rate each item ("I have someone who will listen to me when I need to talk," "I have someone to talk with when I have a bad day") on a scale from 1= "never" to 5= "always."

The PROMIS Instrumental Support Short Form is a 6-item measure used to assess instrumental support. Participants are asked to rate each item (e.g., "Do you have someone to take you to the doctor if you needed it?," "Do you have someone to prepare your meals if you are unable to do it yourself?") on a scale from 1= "never" to 5= "always."

The PROMIS Informational Support Short Form is a 6-item measure used to assess informational support. Participants are asked to rate each item (e.g., "I have someone to turn to for suggestions about how to deal with a problem," "I have someone to give me information if I need it") on a scale from 1= "never" to 5= "always."

Waitlist control participants will receive the intervention and receive systematic training in cognitive and behavioral coping skills approximately 6 months into their participation in the study.

Total of all reporting groups

Waitlist control participants will receive the intervention and receive systematic training in cognitive and behavioral coping skills approximately 6 months into their participation in the study.

Intervention will be evaluated using 3 open-ended questions, including the following: "1) What was the most helpful part of the program?," "2) What was the least helpful part of the program?", and "3) What suggestions do you have for us to help improve the program?"

Participants who completed at least one intervention session.

Treatment feasibility will be assessed by measuring the session attendance rate for each participant.

Any participant who had at least one intervention session was included for analysis.

The Treatment Acceptability Questionnaire is a six-item scale assessing participants' views of an intervention as acceptable, ethical, and effective. Items are rated on a 7-point Likert scale (e.g., 1 "very unacceptable" to 7 "very acceptable") and averaged.

One participant in the waitlist control condition was excluded from analysis due to an incomplete response to the measure.

Participants' use of intervention strategies will be assessed using a measure developed specific to components of the proposed intervention. Participants will be asked about how frequently treatment strategies discussed in session have been used outside of session since the previous session or last assessment depending on the timing of the questionnaire. A scale ranging from 0 "not at all" to 5 "every day" will be used.

Any participant who had at least one intervention session was included for analysis.

Participants' use of the mobile application will be assessed using a measure developed specific to components of the proposed mobile application. Participants will be asked about how frequently they have used components of the mobile application outside of session since the previous session or last assessment depending on the timing of the questionnaire. A scale ranging from 0 "not at all" to 5 "2 or more times a day" will be used.

Any participant who had at least one intervention session was included for analysis.

Depressive Symptoms will be assessed using the Patient Reported Outcomes Measurement Information System Depression Short Form-8a, an 8-item measure assessing symptoms of depression in the last week. Participants are asked to respond to items (e.g., "I felt sad," "I felt helpless") using a five-point scale ranging from 1 "never" to 5 "always." Items are summed and converted to standardized t-scores with a mean of 50 and standard deviation of 10. Higher T-scores indicate higher levels of depression. T-scores of 55 to 60 indicate mild levels of depression, 60 to 70 indicates moderate levels of depression, and greater than 70 indicate severe levels of depression.

Respondents were included if they provided a complete response to the measure. All participants received the intervention.

Symptoms of Anxiety will be assessed using the Patient Reported Outcomes Measurement Information System Anxiety Short Form-8a, an 8-item measure assessing symptoms of anxiety in the last week. Participants are asked to respond to items (e.g., "I felt nervous," "I felt tense") using a five-point scale ranging from 1 "never" to 5 "always". Total scores are then converted to T-scores. Items are summed and converted to standardized t-scores with a mean of 50 and standard deviation of 10. Higher T-scores indicate higher levels of anxiety. T-scores of 55 to 60 indicate mild levels of anxiety, 60 to 70 indicates moderate levels of anxiety, and greater than 70 indicate severe levels of anxiety.

Respondents were included if they provided a complete response to the measure. All participants received the intervention.

Symptom interference will be assessed using the Illness Intrusiveness Rating Scale (IIRS). The IIRS assesses the extent to which an illness and/ or its treatments interfere with 13 quality of life domains (e.g., health, diet, work, sex life, active recreation). Items are rated on a 7-point scale from 1 "not very much" to 7 "very much." The total score ranges from 7 to 91, where a higher score indicates greater interference.

Respondents were included if they provided a complete response to the measure. All participants received the intervention.

The Brief Pain Inventory is a 9-item, self-report measure assessing pain severity and interference from pain across important life domains (e.g., general activity, work, relations with others). Participants rate their pain on a scale from 0 "no pain" to 10 "pain as bad as you can imagine." Pain severity is calculated as the average of four items assessing participants' worst, least, current, and average (in the last week) pain on a scale from 0 "no pain" to 10 "worst pain." Pain interference is computed as the average of seven items, which ask about the interference of pain across different life domains (e.g., general activity, mood, relations with other people).

Respondents were included if they provided a complete response to the measure. All participants received the intervention.

Fatigue will be assessed using the Patient Reported Outcomes Measurement Information System Fatigue Scale, a 6-item self-report measure of fatigue. Participants are asked to think about the last week when responding to each item (e.g., "In the past 7 days, how run-down did you feel, on average?"). Items are summed and converted to standardized t-scores with a mean of 50 and standard deviation of 10. A higher score indicates greater fatigue. T-scores of 55 to 60 indicate mild levels of fatigue, 60 to 70 indicates moderate levels of fatigue, and greater than 70 indicate severe levels of fatigue.

All participants received the intervention.

The International Physical Activity Questionnaire is a seven-item questionnaire that assesses the amount of time participants have spent doing physical activity (e.g., moderate physical activities, vigorous physical activities, walking) in the last seven

The Stanford LCAT is a categorical item that assesses the type of physical activities participants do.

The FACIT assesses the spiritual wellbeing of participants with 12-item questionnaire on a scale from 0 = "not at all" to 4 = "very much."

The AAQ is a 7-item questionnaire to track psychological flexibility related to coping with cancer and cancer treatment. The scale ranges from 1 = "never true" to 7 "always true." Item is scored by adding all of the responses together.

The VQ is a 10-item self-report questionnaire with a scale 0 = "not true at all" to 6 "completely true."

The 17-item Group Therapy Experiences Scale will be used to assess the level of cohesion among group members (e.g., development of positive relationships, comfort level with other group members). Items 1-16 are rated on a 5-point scale with 1 = "strongly agree" to 5 = "strongly disagree." Item 17 is an open-ended question, "was there something in the group today that helped or hindered you?"relationships, comfort level with other group members). Items are rated on a 4-point scale with 1= "strongly disagree" to 4= "strongly agree."

The PROMIS Social Isolation Scale is a 6-item measure is used to assess social isolation. Participants are asked to rate each item (e.g., "I felt left out," "I feel that people avoid talking to me") on a scale from 1= "never" to 5= "always."

The Self-Efficacy for Managing Chronic Disease Scale is a 6-item scale. Participants rate their confidence in keeping pain, fatigue, emotional distress, and other symptoms from interfering with things they want to do on a scale from 1 "not at all confident" to 10 "totally confident."

The PROMIS Self-Efficacy for Managing Chronic Conditions - Managing Symptoms - Short Form 4a is a 4-item scale. Participants rate their confidence in managing their symptoms during daily activities, with relationships with friends and family, in a public place, and working with their doctor to manage these symptoms on a scale from 1 = "I am not at all confident" to 5 "I am very confident."

The PROMIS Emotional Support Short Form is a 6-item measure used to assess emotional support. Participants are asked to rate each item ("I have someone who will listen to me when I need to talk," "I have someone to talk with when I have a bad day") on a scale from 1= "never" to 5= "always."

The PROMIS Instrumental Support Short Form is a 6-item measure used to assess instrumental support. Participants are asked to rate each item (e.g., "Do you have someone to take you to the doctor if you needed it?," "Do you have someone to prepare your meals if you are unable to do it yourself?") on a scale from 1= "never" to 5= "always."

The PROMIS Informational Support Short Form is a 6-item measure used to assess informational support. Participants are asked to rate each item (e.g., "I have someone to turn to for suggestions about how to deal with a problem," "I have someone to give me information if I need it") on a scale from 1= "never" to 5= "always."

Waitlist control participants will receive the intervention and receive systematic training in cognitive and behavioral coping skills approximately 6 months into their participation in the study.

Waitlist control participants will receive the intervention and receive systematic training in cognitive and behavioral coping skills approximately 6 months into their participation in the study.