The inclusion criteria for participants are:  Men and women, aged between 18 and 70 years. Cancer diagnosis, stages I-III. Cancer type: Breast / Lung / Colorectal. Eligible for or currently receiving cancer treatment. Ability to be fluent in Spanish. Have a smartphone with daily access and basic smartphone / application management skills. Access to email account and internet. Not currently participating in another clinical trial. Not currently receiving other psychological treatment.  Exclusion criteria for participants in the trial:  Men and women aged> 70 years. Diagnosis of cancer, stage IV or other types of cancer. Not eligible for treatment. Inability to handle himself fluently in Spanish. Not having a smartphone with daily access and basic smartphone / application skills. Not having access to an email account and the internet. Currently participating in another clinical trial. Currently receiving other psychological treatment.