Experimental: Heart-rate variability (HRV) biofeedback intervention + standard of care Deep paced breathing with the HRV monitoring performed three times a day for seven minutes during three months with standard of care.

Cohort A- breast cancer, Cohort B- colon cancer

Cohort A- neoadjuvant chemotherapy +/- targeted therapy +/- immunotherapy defined standard of care in current European Society For Medical Oncology (ESMO) guideline in the defined disease subtype Cohort B- adjuvant chemotherapy +/- targeted therapy +/- immunotherapy defined standard of care in current ESMO guideline in the defined disease subtype

Daily deep paced breathing 3-times (minimum 7 minutes each) for 3 months

he effect of 3-month heart rate variability (HRV) biofeedback training and conventional cancer treatment (standard of care, SOC) vs. SOC alone on inflammation (IL-6, Tumor necrosis factor α, IL-10 from peripheral blood sample in pg/ml and tumour infiltrating lymphocytes (TIL) in %).

Effect of HRV biofeedback training on quality of life (HRV biofeedback + SOC, vs. The effect of 3-month heart rate variability (HRV) biofeedback training and conventional cancer treatment (standard of care, SOC) vs. SOC alone on EORTC-QLQ-C30 (version 3) score (QLQ- Quality Life Questionnaire). The EORTC-QLQ-C30 has 30 items divided into five functional scales (physical, role, cognitive, emotional, and social), and three symptom scales (fatigue, pain, and nausea and vomiting). The score for each scale as well as the sum score for the whole instrument is standardized to values 0 to 100, with a higher score meaning a worse outcome.

Effect of HRV biofeedback training on executive functions (HRV biofeedback + SOC, vs. SOC alone) measured by Stroop task mean response time for color-word condition.

The effect of 3-month heart rate variability (HRV) biofeedback training and conventional cancer treatment (standard of care, SOC) vs. SOC alone on salivary cortisol slopes (difference between bedtime and awakening saliva cortisol concentration in ng/ml).

The effect of 3-month heart rate variability (HRV) biofeedback training and conventional cancer treatment (standard of care, SOC) vs. SOC alone on sleep quality measured by both actigraphy and self-report data. The main variables are total time spent sleeping (in hours and minutes), and sleep efficiency (proportion of time spent sleeping vs. time spent in bed trying to sleep).

The effect of 3-month heart rate variability (HRV)biofeedback training and conventional cancer treatment (standard of care, SOC) vs. SOC alone on pCR rate evaluated pathologically in surgical specimen after neoadjuvant therapy, value pCR, RCB I, RCB II, RCB III.