Standard of care includes medical treatment at Landspitali University Hospital, and optional cancer rehabilitation at the Ljósið Cancer Rehabilitation Center.

Difference in change in the total score on the European Organization for the Research and Treatment of Cancer Quality of Life Questionnaire Fatigue Module (EORTC-QLQ-FA12) between the intervention and control groups.

This 12-item questionnaire assesses physical-, cognitive- and emotional fatigue, the questionnaire is composed of 12 questions with a Likert scale of 4 options where 1 represents "not at all" to 4 "very much". Scores on the EORTC-QLQ-FA12 range from 12 to 48, with a lower score representing less fatigue.

Difference in change in the scores on the European Organization for the Research and Treatment of Cancer Quality of Life Questionnaire for Prostate Cancer (EORTC-QLQ-PR25) between the prostate cancer patients in the intervention and control groups.

The EORTC QLQ-PR25 questionnaire assesses symptoms related to prostate cancer, its treatment, and aspects of life related to this type of cancer. It consists of 25 questions with a Likert scale of 4 options where 1 represents "not at all," to 4 "very." The questions included in the questionnaire are grouped into symptom scales (questions 1 to 19) and functional scales (questions 20-25).

For the EORTC QLQ-PR25 questionnaire, a higher score on the symptomatic scales means a greater severity of symptoms, while a higher score on question 20-22 and a lower score on questions 23-25 of the functional scales means a higher level of functioning.

Difference in change in the total score on the European Organization for the Research and Treatment of Cancer Quality of Life Questionnaire for Lung Cancer (EORTC-QLQ-LC13) between the lung cancer patients in the intervention and control groups.

The EORTC-QLQ-LC13 is a 13-item questionnaire. It is composed of 13 questions with a Likert scale of 4 options where 1 represents "not at all" to 4 "very much". Scores on the EORTC-QLQ-LC13 range from 13 to 52, with a lower score representing a higher quality of life.

Difference in change in the total score on the European Organization for the Research and Treatment of Cancer Quality of Life Questionnaire for Colorectal Cancer (EORTC-QLQ-CR29) between the colorectal cancer patients in the intervention and control groups.

The EORTC-QLQ-CR29 is a 29-item questionnaire. It is composed of 29 questions with a Likert scale of 4 options where 1 represents "not at all" to 4 "very much", with some of these questions specific for people with or without a stoma bag, and two specific questions for each sex. Scores on the EORTC-QLQ-CR29 range from 25 to 104 with a lower score (on all but one of the two specific questions for each sex) representing a higher quality of life.

Difference in change in the total score of the 21-item Depression, Anxiety and Stress Scale (DASS21) questionnaire between the intervention and control group.

Each question has a Likert scale of 4 options where 0 represents "did not apply to me" to 3 "applied to me very much". The scores on the subscales range from 0 to 63, and low scores indicate a better mental health status.

Evaluate the difference in cancer- and treatment-specific side effects in the intervention group between baseline and end of intervention.

Side effects are measured through in-app patient reported outcomes (PROs): patients evaluate their symptoms, grading them on a scale of 1 to 10, where low scores indicate the mildest symptoms and high scores indicate the most severe symptoms.

Evaluate the difference in sleep, energy, and stress levels in the intervention group between base line and end of intervention.

Sleep, energy, and stress levels are measured through in-app patient reported outcomes (PROs). Patients score their sleep, energy, and stress levels, grading them on a scale of 1 to 10. Low scores indicate poor sleep quality, low energy levels, and low stress levels. High scores indicate good sleep quality, high energy levels, and stress levels.

Difference in change in total score of the self-assessed EuroQuol Five Dimension - Five Level (EQ-5D-5L) health questionnaire between the intervention and control groups EQ-E5-5L scores range from -0.530 to 1, with higher scores indicating a better health status. A score of 1 indicates full health.

Difference in change in a 6-item Self-Efficacy for Managing Chronic Disease questionnaire (SEMCD) score between the intervention and control groups.

The SEMCD covers several domains that are common across many chronic diseases, such as symptom control, role function, emotional functioning, and communicating with physicians.

The SEMCD questionnaire is composed of 6 questions with Likert scales of 10 options where 1 represents "not at all confident" to 10 "totally confident". Scores on the SEMCD range from 6 to 60, with a higher score representing a higher self-efficacy.

Scores in the mHealth App Usability Questionnaire (MAUQ) of the intervention group.

The MAUQ is an 18-item questionnaire. It is composed of questions with Likert scales of 7 options where 1 represents "strongly disagree" to 7 "strongly agree". Scores on the MAUQ range from 18 to 126, with a higher score representing a higher usability.

Percentage of participants that will complete the digital intervention (DTx) program. Where "complete" is defined as finishing 75% of program.

Percentage of participants that are active in the digital intervention (DTx) program. Where "active" is defined as visiting the app at least once per week.