Here is the design of a clinical trial:

Official Title: The Modulatory Role of Internet-supported Mindfulness-based Cognitive Therapy on Extracellular Vesicles and Psychological Distress in People Who Have Had Cancer: A Study Protocol for a Two-armed Randomized Controlled Trial

Included conditions:
- Cancer

Study Armgroups:
- {'label': 'Mindfulness Based Cognitive Therapy (MBCT)', 'type': 'EXPERIMENTAL', 'description': 'Group intervention on Mindfulness-Based Cognitive Therapy classic program plus 4 monthly consolidation sessions of 90 minutes each.', 'interventionNames': ['Behavioral: Mindfulness Based Cognitive Therapy (MBCT)']}
- {'label': 'Treatment as Usual (TAU)', 'type': 'OTHER', 'description': 'TAU will be the control condition.', 'interventionNames': ['Other: Treatment as Usual']}

Interventions:
- {'type': 'BEHAVIORAL', 'name': 'Mindfulness Based Cognitive Therapy (MBCT)', 'description': "Experimental group: MBCT is program developed by Zindel Segal, Mark Williams, and John Teasdale , based on Jon Kabat-Zinn's Mindfulness-based Stress Reduction (MBSR) program. Participants learn to acknowledge their unhelpful thoughts and feelings, allowing the mind to move from an automatic and spiraling thought pattern to a more conscious emotional processing. Mindfulness practices include breath awareness, sitting and walking meditations, and mindful yoga. In this study, the following MBCT structure will be followed: group setting of 12 participants (maximum); 8 online weekly meetings of 2 hours via a videoconference platform (e.g., Cisco Webex), each one mediated by a trained mindfulness instructor(s); daily home practice of the learned skills; 2 hours of retreat after the fifth week; 6 months of home practice; 4 monthly consolidation sessions of 90 minutes each.", 'armGroupLabels': ['Mindfulness Based Cognitive Therapy (MBCT)']}
- {'type': 'OTHER', 'name': 'Treatment as Usual', 'description': 'In this case, participants will follow the usual institutional intervention protocol for medical follow-up and identification, referral, and intervention for people with significant distress difficulties. Regarding pharmacological intervention, medication intake will be monitored during the study and changes will be registered. The engagement in non-pharmacological interventions such as psychological and psychosocial interventions will also be monitored.', 'armGroupLabels': ['Treatment as Usual (TAU)']}

Primary Outcomes:
- {'measure': 'Change on Extracellular Vesicles', 'description': 'Isolated by ultracentrifugation with sucrose cushion. The collected EVs will be quantified by Nanoparticle tracking analysis (Nanosight Ltd.), and data will be measured in particles per milliliter (mL).', 'timeFrame': 'T1 - before intervention; 8 weeks after T1; 24 weeks after T1'}
- {'measure': 'Change on Distress', 'description': 'Measured with Depression Anxiety Stress Scales-21 - DASS-21, a self-report and public domain questionnaire that evaluates negative affective states. It is composed of 21 items, 7 focused on depression, 7 on anxiety, and 7 on stress. Each item is rated on a 4-point Likert-type scale, wherein in 0 represents "did not apply to me at all" and 3 represents "applied to me very much or most of the time". The score for each subscale ranges between 0 and 21. In the current study, a total score will be computed by summing all items, with higher scores being indicative of higher self-reported psychological distress.', 'timeFrame': 'T1- before intervention; T2 - 4 weeks after baseline; T3 - 8 weeks after baseline; T4 - 24 weeks after baseline; T5 - 52 weeks after baseline'}

Please estimate the sample size based on the assumption: 
Alpha significance level of 0.05, power of 0.80, and dropout rates ranging from 12.1% to 32% for the intervention group and 6% to 17.4% for the control group, with follow-up dropout rates of about 30.8% and 19.6% respectively.
Sample size estimation
          Because no previous study has examined circulating EVs in relation to MBIs and cancer, we could not use a specific effect size in estimating the sample size. Nonetheless, a recent systematic review examining the effects of Internet-based MBIs on psychological distress (anxiety and depression) found a median Cohenâs d value between 0.38 and 0.42 for the other primary outcome, psychological distress [14]. By using G*Power-3.1 statistical software [82] and considering repeated-measures ANOVA related to within-between interaction (group Ã time interaction), with an alpha significance level of 0.05 and an effect size of 0.38 (as calculated in [83]), a sample of 84 participants would allow for a power of 0.80. Additionally, previous studies showed dropout rates ranging from 12.1 to 32% for the intervention group and from 6 and 17.4% for the control group, when considering the period immediately following the intervention [23, 32, 40, 47, 49, 52, 84]. At follow-up, dropout rates were about 30.8% in the intervention group and 19.6% in the control group [52]. Considering the highest dropout rate (32%), 27 participants should be added to the estimated sample, resulting in a minimum of 111 participants to be included in the study.