In this trial, the investigators introduce two internet-based psychological methods to meet the currently unmet medical need to cope with Fear of Cancer Recurrence (FCR) beyond the acute phase of cancer treatment: internet-based emotional freedom techniques (iEFT) and internet-based mindfulness intervention (iMMI). The primary aim of this trial is to examine the efficacy of Internet-Based Emotional Freedom Techniques (iEFT) and Internet-Based Mindfulness Meditation Intervention (iMMI) to alleviate Fear of Cancer Recurrence (FCR) in cancer survivors, as determined through the Fear of Cancer Recurrence Inventory (FCRI) in cancer survivors. To translate a statistically significant effect on FCR into a clinically significant change, the investigators would need to detect a between-group difference in mean FCRI at T1 of 10 points using an independent samples t-test (two experimental groups are compared against a single wait-list control). When the application of iEFT and/or iMMI appears effective to reduce FCR, these self-help methods could be implemented in clinical settings. The use of these low cost interventions with a low threshold, by an internet-based approach, will facilitate a potential implementation in clinical practice.

Despite our adequate medical care and financial support systems, the mental wellbeing and quality of life after cancer diagnosis and treatment is often poorly addressed in clinical settings. Previous research showed that Fear of Cancer Recurrence (FCR) is one of the most common psychological burdens faced by 39%-97% of cancer survivors. In this phase III randomized multicentre trial, patients will be allocated to either the iEFT group, iMMI group or wait-list control (WLC) group for a study trajectory of 6 weeks. 339 cancer survivors, between 6 months and 5 years since diagnosis, and who have completed their primary cancer treatment (i.e. surgery, radiation, and/or chemotherapy) will be enrolled and randomized 1:1:1 to one of the two intervention groups or the WLC group. Participants will complete evaluation questionnaires at baseline (T0), after 6 weeks (T1) and 12 weeks (T2) of intervention or waiting list, and 24 weeks (T3). A biomarker endpoint includes the measurement of chronic biologic stress in hair cortisol concentration. Therefore, optional hair collection may take place before (T0) and after the 6-week intervention (T1). Primary objective is to evaluate the feasibility and efficacy of iEFT and iMMI as an intervention strategy to reduce FCR in cancer survivors. The investigators hypothesize that an intervention with iEFT or iMMI will be superior compared to the WLC group at T1. Secondary objectives include the following:

Inclusion Criteria:

• Patients should have reached a minimum age of 18 years at the time of enrolment
• Patients should have a histologically confirmed diagnosis of a solid cancer or haematologic malignancy
• Patients should have completed surgery, chemotherapy, radiation therapy, immunotherapy, hormone therapy, targeted drug therapy or a combination of these at least 2 months ago and no longer than 5 years ago at the time of enrolment
• Patients should have an expected life expectancy of at least 5 years
• Patients are disease-free at the time of enrolment, as defined by the absence of somatic disease activity parameters
• Patients can be included in a stable phase of their immunotherapy (e.g. adjuvant use of checkpoint inhibitors for melanoma), hormonal therapy (e.g. for breast and prostate cancer), targeted drug therapy (e.g. trastuzumab and pertuzumab for breast cancer; stable dose of PARP inhibitors for ovarian cancer; retuximab for lymphoma), or a combination of these
• Patients must suffer from high FCR based on the Cancer Worry Scale (cut-off ≥ 14)
• Patients should be able to adequately communicate in Dutch
• Patients should present with a sufficient mental and physical functional status (according to investigator's judgment and first baseline assessment) for completing the questionnaires and neuropsychological assessment
• Patients under current treatment for a depression or anxiety disorder are allowed to enrol provided their depression or anxiety disorder is stable

Exclusion Criteria:

• Patients who received a treatment with palliative intent
• Patients showing signs of mental deterioration
• Patients suffering from organic brain syndrome (concussion without neurological symptoms and negative imaging is allowed)
• Patients who are alcohol or drug dependent
• Patients with another serious or chronic medical, neurologic or psychiatric condition that contributes to substantial physical or emotional disability that would detract from participating in either of the intervention programmes or from the measurement of intervention outcomes; a prior diagnosis of a depressive, anxiety or adjustment disorder is allowed
• Patients who cannot commit to the intervention schedule; obstacles such as surgery or long-term hospitalisation, change of residence or work, … can have an emotional and practical impact which makes these patients not eligible for participation.
• Patients who actively practice EFT or mindfulness(based) meditation

At the moment, there is no plan to make individual participant data (IPD) available to other researchers. Moreover, data will be pseudonimyzed.